Resist composition and method of forming resist pattern

ABSTRACT

A resist composition including a base component (A) which exhibits changed solubility in a developing solution under the action of acid and an acid-generator component (B) which generates acid upon exposure, the base component (A) containing a polymeric compound (A1) including a structural unit (a0) represented by general formula (a0-1) and a structural unit (a1) containing an acid decomposable group which exhibits increased polarity by the action of acid (R 1  represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W represents —COO—, a —CONH— group or a divalent aromatic hydrocarbon group; Y 1  and Y 2  represent a divalent linking group or a single bond; R′ 1  represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms; R′ 2  represents a monovalent aliphatic hydrocarbon group; and R 2  represents an —SO 2 — containing cyclic group).

TECHNICAL FIELD

The present invention relates to a resist composition which exhibits excellent lithography properties, and a method of forming a resist pattern using the resist composition.

Priority is claimed on Japanese Patent Application No. 2012-066367, filed Mar. 22, 2012, the content of which is incorporated herein by reference.

DESCRIPTION OF RELATED ART

Techniques (pattern-forming techniques) in which a fine pattern is formed on top of a substrate, and a lower layer beneath that pattern is then fabricated by conducting etching with this pattern as a mask are widely used in the production of semiconductor devices and liquid display device. These types of fine patterns are usually formed from an organic material, and are formed, for example, using a lithography method or a nanoimprint method or the like. In lithography techniques, for example, a resist film composed of a resist material containing a base component such as a resin is formed on a support such as a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. Using this resist pattern as a mask, a semiconductor or the like is produced by conducting a step in which the substrate is processed by etching.

The aforementioned resist material can be classified into positive types and negative types. Resist materials in which the exposed portions exhibit increased solubility in a developing solution is called a positive type, and a resist material in which the exposed portions exhibit decreased solubility in a developing solution is called a negative type.

In general, an aqueous alkali solution (alkali developing solution) such as an aqueous solution of tetramethylammonium hydroxide (TMAH) is used as the developing solution (hereafter, the process using an alkali developing solution is sometimes referred to as “alkali developing process”).

In recent years, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.

Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as electron beam (EB), extreme ultraviolet radiation (EUV), and X ray.

As shortening the wavelength of the exposure light source progresses, it is required to improve various lithography properties of the resist material, such as the sensitivity to the exposure light source and a resolution capable of reproducing patterns of minute dimensions. As resist materials which satisfy such requirements, chemically amplified resists are known.

As a chemically amplified composition, a composition including a base material component that exhibits a changed solubility in a developing solution under the action of acid and an acid-generator component that generates acid upon exposure is generally used. For example, in the case of an alkali developing process, a base component which exhibits increased solubility in an alkali developing solution under action of acid is used.

Conventionally, a resin (base resin) is typically used as the base component of a chemically amplified resist composition. Resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are the mainstream as base resins for chemically amplified resist compositions that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm.

Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.

In general, the base resin contains a plurality of structural units for improving lithography properties and the like. For example, a structural unit having a lactone structure and a structural unit having a polar group such as a hydroxy group are used, as well as a structural unit having an acid decomposable group which is decomposed by the action of an acid generated from the acid generator to form an alkali soluble group (for example, see Patent Document 1). When the base resin is an acrylic resin, as the acid decomposable group, in general, resins in which the carboxy group of (meth)acrylic acid or the like is protected with an acid dissociable group such as a tertiary alkyl group or an acetal group are used.

In a positive tone development process using a positive type, chemically amplified resist composition (i.e., a chemically amplified resist composition which exhibits increased alkali solubility in an alkali developing solution upon exposure) in combination with an alkali developing solution, as described above, the exposed portions of the resist film are dissolved and removed by an alkali developing solution to thereby form a resist pattern. The positive tone process is advantageous over a negative tone development process in which a negative type, chemically amplified resist composition is used in combination with an alkali developing solution in that the structure of the photomask can be simplified, a satisfactory contrast for forming an image can be reliably obtained, and the characteristics of the formed resist pattern are excellent. For these reasons, currently, positive tone development process is tended to be used in the formation of an extremely fine resist pattern.

However, in the case of forming a trench pattern (isolated space pattern) or a hole pattern by the positive tone development process, it becomes necessary to form a resist pattern using an incident light weaker than that used in the case of a line pattern or a dot pattern, such that the contrast of the intensity of the incident light between exposed portions and unexposed portions becomes unsatisfactory. Therefore, pattern formation performance such as resolution tends to be restricted, and it becomes difficult to form a resist pattern with a high resolution.

In contrast, a negative tone development process using a negative type, chemically amplified resist composition (i.e., a chemically amplified resist composition which exhibits decreased alkali solubility in an alkali developing solution upon exposure) in combination with an alkali developing solution is advantageous over the positive tone development process in the formation of a trench pattern or a hole pattern.

In recent years, as a negative tone development process, a process has been proposed in which a positive type, chemically amplified resist composition is used in combination with a developing solution containing an organic solvent (hereafter, frequently referred to as “organic developing solution”) (hereafter, the process using an organic developing solution is sometimes referred to as “solvent developing process” or “negative-tone solvent developing process”). A positive type, chemically amplified resist composition exhibits increased solubility in an alkali developing solution upon exposure, but comparatively, the solubility in an organic solvent is decreased. Therefore, in a negative-tone solvent developing process, the unexposed portions of the resist film are dissolved and removed by an organic solvent-type developing solution to thereby form a resist pattern (see, for example, Patent Document 2).

DOCUMENTS OF RELATED ART Patent Document

-   [Patent Document 1] Japanese Unexamined Patent Application, First     Publication No. 2003-241385 -   [Patent Document 2] Japanese Unexamined Patent Application, First     Publication No. 2009-025723

SUMMARY OF THE INVENTION

As miniaturization of resists progress, there is still room for improvement in the lithography properties of the conventional resist materials. In the formation of a resist pattern, a resist composition which exhibits excellent lithography properties and can be used in both alkali developing process and negative-tone solvent developing process has been demanded. In the negative-tone solvent developing process, line collapse becomes a problem.

The present invention takes the above circumstances into consideration, with an object of providing a resist composition which can be used in both alkali developing process and negative-tone solvent developing process, and which exhibits excellent lithography properties with reduced line collapse.

For solving the above-mentioned problems, the present invention employs the following aspects.

Specifically, a first aspect of the present invention is a resist composition including a base component (A) which exhibits changed solubility in a developing solution under the action of acid and an acid-generator component (B) which generates acid upon exposure, the base component (A) containing a polymeric compound (A1) including a structural unit (a0) represented by general formula (a0-1) shown below and a structural unit (a1) containing an acid decomposable group which exhibits increased polarity by the action of acid.

In the formula, R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W represents —COO—, a —CONH— group or a divalent aromatic hydrocarbon group; Y¹ and Y² each independently represents a divalent linking group or a single bond; represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms; R′² represents a monovalent aliphatic hydrocarbon group which may have a substituent; and R² represents an —SO₂-containing cyclic group.

A second aspect of the present invention is a method of forming a resist pattern, including: using a resist composition of the first aspect to form a resist film on a substrate; conducting exposure of the resist film; and developing the resist film to form a resist pattern.

In the present description and claims, an “alkyl group” includes linear, branched or cyclic, monovalent saturated hydrocarbon, unless otherwise specified.

The term “alkylene group” includes linear, branched or cyclic divalent saturated hydrocarbon, unless otherwise specified.

A “halogenated alkyl group” is a group in which part or all of the hydrogen atoms of an alkyl group is substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

The term “aliphatic” is a relative concept used in relation to the term “aromatic”, and defines a group or compound that has no aromaticity.

The term “structural unit” refers to a monomer unit that contributes to the formation of a polymeric compound (polymer, copolymer).

The term “exposure” is used as a general concept that includes irradiation with any form of radiation.

According to the present invention, there is provided a resist composition which can be used in both alkali developing process and negative-tone solvent developing process, and which exhibits excellent lithography properties with reduced line collapse.

DETAILED DESCRIPTION OF THE INVENTION

<<Resist Composition>>

The resist composition according to a first aspect of the present invention includes a base component (A) which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid (hereafter, sometimes referred to as “component (A)”).

By virtue of containing the component (A), the resist composition of the present invention has a characteristic of exhibiting changed solubility in a developing solution upon exposure. When a resist film is formed using the resist composition, and the resist film is subjected to a selective exposure, acid is generated from the component (A) at exposed portions, and the generated acid acts on the component (A) to change the solubility of the component (A) in a developing solution. As a result, the solubility of the exposed portions in a developing solution is changed, whereas the solubility of the unexposed portions in a developing solution remain unchanged. Therefore, by subjecting the resist film to development, the exposed portions are dissolved and removed to form a positive-tone resist pattern in the case of a positive resist, whereas the unexposed portions are dissolved and removed to form a negative-tone resist pattern in the case of a negative resist.

In the present specification, a resist composition which forms a positive resist pattern by dissolving and removing the exposed portions is called a positive resist composition, and a resist composition which forms a negative resist pattern by dissolving and removing the unexposed portions is called a negative resist composition.

The resist composition of the present invention may be either a positive resist composition or a negative resist composition. Further, in the formation of a resist pattern, the resist composition of the present invention can be applied to an alkali developing process using an alkali developing solution in the developing treatment, or a solvent developing process using a developing solution containing an organic solvent (organic developing solution) in the developing treatment. The resist composition of the present invention is preferably used in the formation of a positive-tone resist pattern by an alkali developing process and a negative-tone resist pattern by a solvent developing process. In such a case, as the component (A), a base component that exhibits increased solubility in an alkali developing solution (decreased solubility in an organic developing solution) under the action of acid is used.

<Component (A)>

The component (A) used in the resist composition of the present invention is a base component which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid, and contains a polymeric compound (A1) (hereafter, sometimes referred to as “component (A1)”) which includes a structural unit (a0) and a structural unit (a1) described later).

Here, the term “base component” refers to an organic compound capable of forming a film, and is preferably an organic compound having a molecular weight of 500 or more. When the organic compound has a molecular weight of 500 or more, the film-forming ability is improved, and a resist pattern of nano level can be easily formed. The “organic compound having a molecular weight of 500 or more” which can be used as a base component is broadly classified into non-polymers and polymers.

In general, as a non-polymer, any of those which have a molecular weight in the range of 500 to less than 4,000 is used. Hereafter, a non-polymer having a molecular weight in the range of 500 to less than 4,000 is referred to as a low molecular weight compound.

As a polymer, any of those which have a molecular weight of 1,000 or more is generally used. Hereafter, a polymer having a molecular weight of 1,000 or more is referred to as a polymeric compound. With respect to a polymeric compound, the “molecular weight” is the weight average molecular weight in terms of the polystyrene equivalent value determined by gel permeation chromatography (GPC). Hereafter, a polymeric compound is frequently referred to simply as a “resin”.

[Component (A1)]

The component (A) contains a polymeric compound (A1) (hereafter, referred to as component (A1)) which includes a structural unit (a0) represented by general formula (a0-1) shown below and a structural unit (a1) containing an acid decomposable group which exhibits increased polarity by the action of acid.

In the formula, R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W represents —COO—, a —CONH— group or a divalent aromatic hydrocarbon group; Y¹ and Y² each independently represents a divalent linking group or a single bond; R′¹ represents a hydrogen atom or an alkyl group of 1 to 6 carbon atoms; R′² represents a monovalent aliphatic hydrocarbon group which may have a substituent; and R² represents an —SO₂-containing cyclic group.

(Structural Unit (a0))

The structural unit (a0) is a structural unit represented by the aforementioned general formula (a0-1).

In formula (a0-1), R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms.

The alkyl group for R¹ is preferably a linear or branched alkyl group of 1 to 5 carbon atoms, and specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group.

The halogenated alkyl group of 1 to 5 carbon atoms represented by R¹ is a group in which part or all of the hydrogen atoms of the aforementioned alkyl group of 1 to 5 carbon atoms have been substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

As a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl group of 1 to 5 carbon atoms is preferable, and a hydrogen atom or a methyl group is particularly desirable in terms of industrial availability.

In formula (a0-1), W represents —COO—, a —CONH— group or a divalent aromatic hydrocarbon group.

The divalent aromatic hydrocarbon group is a divalent hydrocarbon group having at least one aromatic ring, and may have a substituent. The aromatic ring is not particularly limited, as long as it is a cyclic conjugated compound having (4n+2) π electrons (wherein n represents 0 or a natural number), and may be either monocyclic or polycyclic. Examples of the aromatic ring include aromatic hydrocarbon rings such as benzene, naphthalene, anthracene and phenanthrene.

As the divalent aromatic hydrocarbon group, an aromatic hydrocarbon group of 6 to 15 carbon atoms can be mentioned.

Specific examples include groups in which 2 hydrogen atoms have been removed from benzene, naphthalene, anthracene, phenanthrene or pyrene, and a phenylene group or a naphthylene group is preferable. These groups may have a substituent described later.

In formula (a0-1), Y¹ and Y² each independently represents a divalent linking group or a single bond. Y¹ and Y² may be the same or different from each other.

As preferable examples of the divalent linking group for Y¹ and Y², a divalent hydrocarbon group which may have a substituent, and a divalent linking group containing a hetero atom can be given.

(Divalent Hydrocarbon Group which May have a Substituent)

The divalent hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group.

An “aliphatic hydrocarbon group” refers to a hydrocarbon group that has no aromaticity. The aliphatic hydrocarbon group may be saturated or unsaturated. In general, the aliphatic hydrocarbon group is preferably saturated.

As specific examples of the aliphatic hydrocarbon group, a linear or branched aliphatic hydrocarbon group, and an aliphatic hydrocarbon group containing a ring in the structure thereof can be given.

The linear or branched aliphatic hydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 1 to 8, and still more preferably 1 to 5.

As the linear aliphatic hydrocarbon group, a linear alkylene group is preferable. Specific examples thereof include a methylene group [—CH₂—], an ethylene group [—(CH₂)₂—], a trimethylene group [—(CH₂)₃-], a tetramethylene group [—(CH₂)₄—] and a pentamethylene group [—(CH₂)₅—].

As the branched aliphatic hydrocarbon group, branched alkylene groups are preferred, and specific examples include various alkylalkylene groups, including alkylmethylene groups such as —CH(CH₃)—, —CH(CH₂CH₃)—, —C(CH₃)₂—, —C(CH₃)(CH₂CH₃)—, —C(CH₃)(CH₂CH₂CH₃)—, and —C(CH₂CH₃)₂— alkylethylene groups such as —CH(CH₃)CH₂—, —CH(CH₃)CH(CH₃)—, —C(CH₃)₂CH₂—, —CH(CH₂CH₃)CH₂—, and —C(CH₂CH₃)₂—CH₂—; alkyltrimethylene groups such as —CH(CH₃)CH₂CH₂—, and —CH₂CH(CH₃)CH₂—; and alkyltetramethylene groups such as —CH(CH₃)CH₂CH₂CH₂—, and —CH₂CH(CH₃)CH₂CH₂—. As the alkyl group within the alkylalkylene group, a linear alkyl group of 1 to 5 carbon atoms is preferable.

The linear or branched aliphatic hydrocarbon group may or may not have a substituent (a group or atom other than hydrogen) which substitutes the hydrogen atom. Examples of the substituent include a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxo group (═O).

As examples of the hydrocarbon group containing a ring in the structure thereof, a cyclic aliphatic hydrocarbon group containing a hetero atom in the ring structure thereof and may have a substituent (a group in which two hydrogen atoms have been removed from an aliphatic hydrocarbon ring), a group in which the cyclic aliphatic hydrocarbon group is bonded to the terminal of the aforementioned chain-like aliphatic hydrocarbon group, and a group in which the cyclic aliphatic group is interposed within the aforementioned linear or branched aliphatic hydrocarbon group, can be given. As the linear or branched aliphatic hydrocarbon group, the same groups as those described above can be used.

The cyclic aliphatic hydrocarbon group preferably has 3 to 20 carbon atoms, and more preferably 3 to 12 carbon atoms.

The cyclic aliphatic hydrocarbon group may be polycyclic or monocyclic. As the monocyclic aliphatic hydrocarbon group, a group in which 2 hydrogen atoms have been removed from a monocycloalkane is preferable. The monocycloalkane preferably has 3 to 6 carbon atoms, and specific examples thereof include cyclopentane and cyclohexane. As the polycyclic aliphatic hydrocarbon group, a group in which two hydrogen atoms have been removed from a polycycloalkane is preferable, and the polycyclic group preferably has 7 to 12 carbon atoms. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

The cyclic aliphatic hydrocarbon group may or may not have a substituent (a group or atom other than hydrogen) which substitutes the hydrogen atom. Examples of substituents include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group and an oxo group (═O).

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

The cyclic aliphatic hydrocarbon group may have part of the carbon atoms constituting the ring structure thereof substituted with a substituent containing a hetero atom. As the substituent containing a hetero atom, —O—, —C(═O)—O—, —S—, —S(═O)₂— or —S(═O)₂—O— is preferable.

The aromatic group for the divalent hydrocarbon group is the same as defined for the aforementioned aromatic hydrocarbon group for W, and a phenylene group or a naphthylene group is preferable.

The aromatic group may or may not have a substituent. For example, the hydrogen atom bonded to the aromatic ring within the aromatic group may be substituted with a substituent. Examples of substituents include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group and an oxo group (═O).

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

(Divalent Linking Group Containing a Hetero Atom)

With respect to a “divalent linking group containing a hetero atom”, a hetero atom is an atom other than carbon and hydrogen, and examples thereof include an oxygen atom, a nitrogen atom, a sulfur atom, a halogen atom and a silicon atom.

Specific examples of the divalent linking group containing a hetero atom include non-hydrocarbon linking groups such as —O—, —C(═O)—, —C(═O)—O—, —O—C(═O)—O—, —S—, —S(═O)₂—, —S(═O)₂—O—, —NH—, —NH—C(═O)—, —NH—C(═NH)—, ═N— and —SiH₂—O—; and a combination of any one of these non-hydrocarbon linking groups with a divalent hydrocarbon group. The divalent hydrocarbon group is the same as defined for the aforementioned divalent hydrocarbon group which may have a substituent. As the combination, it is preferable to select from an alkylene group, a phenylene group, a naphthylene group, —O—, —C(═O)— and —C(═O)—O—.

Among these, as Y¹ and Y², a single bond or an arylene group such as a phenylene group or a naphthylene group is preferable.

In formula (a0-1), the alkyl group of 1 to 6 carbon atoms for R′¹ is preferably the aforementioned alkyl group of 1 to 5 carbon atoms, a cyclopentyl group or a cyclohexyl group.

As R′¹, a hydrogen atom, a methyl group or an ethyl group is preferable, and a hydrogen atom is more preferable.

R′² represents a monovalent aliphatic hydrocarbon group which may have a substituent. The aliphatic hydrocarbon group for R′² may be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group. Further, the aliphatic hydrocarbon group may be linear, branched or cyclic.

Among these, a linear, branched or cyclic, saturated aliphatic hydrocarbon group is preferable. In the aliphatic hydrocarbon group for R′², part of the carbon atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a hetero atom, or part or all of the hydrogen atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a hetero atom.

As the “hetero atom” for R′², there is no particular limitation as long as it is an atom other than carbon and hydrogen.

Examples of the halogen atom include a fluorine atom, a chlorine atom, an iodine atom and a bromine atom.

The substituent group containing a hetero atom may consist of a hetero atom, or may be a group containing a group or atom other than a hetero atom.

Specific examples of the substituent group for substituting part of the carbon atoms include —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (the H may be replaced with a substituent such as an alkyl group or an acyl group), —S—, —S(═O)₂— and —S(═O)₂—O—. When the aliphatic hydrocarbon group is cyclic, the aliphatic hydrocarbon group may contain any of these substituent groups in the ring structure.

Examples of the substituent group for substituting part or all of the hydrogen atoms include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) and a cyano group.

The aforementioned alkoxy group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the aforementioned halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Example of the aforementioned halogenated alkyl group includes a group in which part or all of the hydrogen atoms within an alkyl group of 1 to 5 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group) have been substituted with the aforementioned halogen atoms.

As the aliphatic hydrocarbon group, a linear, branched or cyclic, saturated hydrocarbon group is preferable.

The linear saturated hydrocarbon group (alkyl group) preferably has 1 to 20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 5. Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, an isotridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group and a docosyl group.

The branched saturated hydrocarbon group (alkyl group) preferably has 3 to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to 10. Specific examples include a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group. As the cyclic saturated hydrocarbon group (alkyl group), a cyclopentyl group or a cyclohexyl group is preferable.

Examples of the substituent for R′² include a halogen atom, an oxy group (═O), a cyano group, an alkyl group, an alkoxyalkyloxy group, an alkoxycarbonylalkyloxy group, —C(═O)—O—R⁷″, —O—C(═O)—R⁸″, —O—R⁹″, —NH— and an aryl group.

R⁷″, R⁸″ and R⁹″ each independently represents a hydrogen atom or a hydrocarbon group.

Examples of the halogen atom as the substituent include a fluorine atom, an iodine atom and a bromine atom, and a fluorine atom is preferable.

In formula (a0-1), as R′², a linear or cyclic alkyl group is preferable. In the case where R′¹ and R′² represent an alkyl group, and R′² may be mutually bonded to form a ring.

In general formula (a0-1), R² represents a cyclic group containing —SO₂— in the ring structure thereof. More specifically, R² is a cyclic group in which the sulfur atom (S) within the —SO₂— group forms part of the ring skeleton thereof.

The cyclic group for R² refers to a cyclic group including a ring that contains —SO₂— within the ring skeleton thereof, and this ring is counted as the first ring. A cyclic group in which the only ring structure is the ring that contains —SO₂— in the ring skeleton thereof is referred to as a monocyclic group, and a group containing other ring structures is described as a polycyclic group regardless of the structure of the other rings. The cyclic group for R² may be either a monocyclic group or a polycyclic group.

As R², a cyclic group containing —O—SO₂— within the ring skeleton thereof, i.e., a cyclic group containing a sultone ring in which —O—S— within the —O—SO₂— group forms part of the ring skeleton thereof is particularly desirable.

The cyclic group for R² preferably has 3 to 30 carbon atoms, more preferably 4 to 20, still more preferably 4 to 15, and most preferably 4 to 12.

Herein, the number of carbon atoms refers to the number of carbon atoms constituting the ring skeleton, excluding the number of carbon atoms within a substituent.

The cyclic group for R² may be either an aliphatic cyclic group or an aromatic cyclic group.

An aliphatic cyclic group is preferable.

Examples of aliphatic cyclic groups for R² include the aforementioned cyclic aliphatic hydrocarbon groups in which part of the carbon atoms constituting the ring skeleton thereof has been substituted with —SO₂— or —O—SO₂—.

More specifically, examples of monocyclic groups include a monocycloalkane in which one hydrogen atom have been removed therefrom and a —CH₂— group constituting the ring skeleton thereof has been substituted with —SO₂—; and a monocycloalkane in which one hydrogen atom have been removed therefrom and a —CH₂—CH₂— group constituting the ring skeleton thereof has been substituted with —O—SO₂—. Examples of polycyclic groups include a polycycloalkane (a bicycloalkane, a tricycloalkane, a tetracycloalkane or the like) in which one hydrogen atom have been removed therefrom and a —CH₂— group constituting the ring skeleton thereof has been substituted with —SO₂—; and a polycycloalkane in which one hydrogen atom have been removed therefrom and a —CH₂—CH₂— group constituting the ring skeleton thereof has been substituted with —O—SO₂—.

The cyclic group for R² may have a substituent. Examples of the substituent include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, an oxygen atom (═O), —COOR″, —OC(═O)R″, a hydroxyalkyl group and a cyano group.

The alkyl group for the substituent is preferably an alkyl group of 1 to 6 carbon atoms. Further, the alkyl group is preferably a linear alkyl group or a branched alkyl group. Specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group and a hexyl group. Among these, a methyl group or ethyl group is preferable, and a methyl group is particularly desirable.

As the alkoxy group for the substituent, an alkoxy group of 1 to 6 carbon atoms is preferable. Further, the alkoxy group is preferably a linear or branched alkoxy group. Specific examples of the alkoxy group include the aforementioned alkyl groups for the substituent having an oxygen atom (—O—) bonded thereto.

Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

As examples of the halogenated alkyl group for the substituent, groups in which part or all of the hydrogen atoms of the aforementioned alkyl groups for the substituent have been substituted with the aforementioned halogen atoms can be given. As the halogenated alkyl group, a fluorinated alkyl group is preferable, and a pertluoroalkyl group is particularly desirable.

In the —COOR″ group and the —OC(═O)R″ group, R″ represents a hydrogen atom or a linear, branched or cyclic alkyl group of 1 to 15 carbon atoms.

When R″ represents a linear or branched alkyl group, it is preferably an alkyl group of 1 to 10 carbon atoms, more preferably an alkyl group of 1 to 5 carbon atoms, and most preferably a methyl group or an ethyl group.

When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

The hydroxyalkyl group for the substituent preferably has 1 to 6 carbon atoms, and specific examples thereof include the aforementioned alkyl groups for the substituent in which at least one hydrogen atom has been substituted with a hydroxy group.

More specific examples of R² include groups represented by general formulas (3-1) to (3-4) shown below.

In the formulas, A′ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; a represents an integer of 0 to 2; and R⁸ represents an alkyl group, an alkoxy group, a halogenated alkyl group, a hydroxyl group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group, wherein R″ represents a hydrogen atom or an alkyl group.

In general formulas (3-1) to (3-4) above, A′ represents an oxygen atom (—O—), a sulfur atom (—S—) or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom.

As the alkylene group of 1 to 5 carbon atoms represented by A′, a linear or branched alkylene group is preferable, and examples thereof include a methylene group, an ethylene group, an n-propylene group and an isopropylene group.

Examples of alkylene groups that contain an oxygen atom or a sulfur atom include the aforementioned alkylene groups in which —O— or —S— is bonded to the terminal of the alkylene group or present between the carbon atoms of the alkylene group. Specific examples of such alkylene groups include —O—CH₂—, —CH₂—O—CH₂—, —S—CH₂—, —CH₂—S—CH₂—.

As A′, an alkylene group of 1 to 5 carbon atoms or —O— is preferable, more preferably an alkylene group of 1 to 5 carbon atoms, and most preferably a methylene group.

a represents an integer of 0 to 2, and is most preferably 0.

When a is 2, the plurality of R⁸ may be the same or different from each other.

As the alkyl group, alkoxy group, halogenated alkyl group, halogenated alkyl group, hydroxyl group, —COOR″, —OC(═O)R″, hydroxyalkyl group and cyano group for R⁸, the same alkyl groups, alkoxy groups, halogenated alkyl groups, halogenated alkyl groups, hydroxyl groups, —COOR″, —OC(═O)R″, hydroxyalkyl groups and cyano groups as those described above as the substituent which the cyclic group for R³ may have can be used.

Specific examples of the cyclic groups represented by general formulas (3-1) to (3-4) are shown below.

In the formulas shown below, “Ac” represents an acetyl group.

Among the examples shown above, as R², a group represented by the aforementioned general formula (3-1), (3-3) or (3-4) is preferable, and a cyclic group represented by the aforementioned general formula (3-1) is particularly desirable.

More specifically, as R², it is preferable to use at least one cyclic group selected from the group consisting of groups represented by chemical formulas (3-1-1), (3-1-18), (3-3-1) and (3-4-1) above, and a group represented by the aforementioned chemical formula (3-1-1) is particularly desirable.

In the present invention, as the structural unit (a0), a structural unit represented by any one of general formulae (a0-1-11) to (a0-1-18) shown below is particularly desirable.

In the formulae, R¹ and A′ are the same as defined above.

A′ is preferably a methylene group, an oxygen atom (—O—) or a sulfur atom (—S—).

As the structural unit (a0), one type of structural unit may be used alone, or two or more types of structural units may be used in combination.

In terms of achieving excellent properties with respect to MEF, the shape of a formed resist pattern (e.g., the rectangularity of a line pattern, the circularity of a hole pattern, and the like), critical dimension uniformity (CDU), line width roughness (LWR) and the like in the formation of a resist pattern using a resist composition containing the component (A1), the amount of the structural unit (a0) within the component (A1), based on the combined total of all structural units constituting the component (A1) is preferably 1 to 60 mol %, more preferably 5 to 55 mol %, and still more preferably 10 to 50 mol %.

(Structural Unit (a1))

The structural unit (a1) is a structural unit which does not fall under the definition of the structural unit (a0), and contains an acid decomposable group that exhibits increased polarity by the action of acid.

The term “acid decomposable group” refers to a group in which at least a part of the bond within the structure thereof is cleaved by the action of acid generated upon exposure (acid generated from the component (B) described later).

Examples of acid decomposable groups which exhibit increased polarity by the action of an acid include groups which are decomposed by the action of an acid to form a polar group.

Examples of the polar group include a carboxy group, a hydroxy group, an amino group and a sulfo group (—SO₃H). Among these, a polar group containing —OH in the structure thereof (hereafter, referred to as “OH-containing polar group”) is preferable, a carboxy group or a hydroxy group is more preferable, and a carboxy group is particularly desirable.

More specifically, as an example of an acid decomposable group, a group in which the aforementioned polar group has been protected with an acid dissociable group (such as a group in which the hydrogen atom of the OH-containing polar group has been protected with an acid dissociable group) can be given.

An “acid dissociable group” is a group in which at least the bond between the acid dissociable group and the adjacent carbon atom is cleaved by the action of acid generated upon exposure. It is necessary that the acid dissociable group that constitutes the acid decomposable group is a group which exhibits a lower polarity than the polar group generated by the dissociation of the acid dissociable group. Thus, when the acid dissociable group is dissociated by the action of acid, a polar group exhibiting a higher polarity than that of the acid dissociable group is generated, thereby increasing the polarity. As a result, the polarity of the entire component (A1) is increased. By the increase in the polarity, the solubility in an alkali developing solution changes and, the solubility in an alkali developing solution is relatively increased, whereas the solubility in a developing solution containing an organic solvent (organic solvent) is relatively decreased.

The acid dissociable group is not particularly limited, and any of the groups that have been conventionally proposed as acid dissociable groups for the base resins of chemically amplified resists can be used. Generally, groups that form either a cyclic or chain-like tertiary alkyl ester with the carboxyl group of the (meth)acrylic acid, and acetal-type acid dissociable groups such as alkoxyalkyl groups are widely known.

Here, a tertiary alkyl ester describes a structure in which an ester is formed by substituting the hydrogen atom of a carboxyl group with a chain-like or cyclic tertiary alkyl group, and a tertiary carbon atom within the chain-like or cyclic tertiary alkyl group is bonded to the oxygen atom at the terminal of the carbonyloxy group (—C(═O)—O—). In this tertiary alkyl ester, the action of acid causes cleavage of the bond between the oxygen atom and the tertiary carbon atom, thereby forming a carboxy group.

The chain-like or cyclic alkyl group may have a substituent.

Hereafter, for the sake of simplicity, groups that exhibit acid dissociability as a result of the formation of a tertiary alkyl ester with a carboxyl group are referred to as “tertiary alkyl ester-type acid dissociable groups”.

Examples of tertiary alkyl ester-type acid dissociable groups include aliphatic branched, acid dissociable groups and aliphatic cyclic group-containing acid dissociable groups.

The term “aliphatic branched” refers to a branched structure having no aromaticity. The “aliphatic branched, acid dissociable group” is not limited to be constituted of only carbon atoms and hydrogen atoms (not limited to hydrocarbon groups), but is preferably a hydrocarbon group. Further, the “hydrocarbon group” may be either saturated or unsaturated, but is preferably saturated. As an example of the aliphatic branched, acid dissociable group, for example, a group represented by the formula —C(R⁷¹)(R⁷²)(R⁷³) can be given. (in the formula, each of R⁷¹ to R⁷³ independently represents a linear alkyl group of 1 to 5 carbon atoms). The group represented by the formula —C(R⁷¹)(R⁷²)(R⁷³) preferably has 4 to 8 carbon atoms, and specific examples include a tert-butyl group, a 2-methyl-2-butyl group, a 2-methyl-2-pentyl group and a 3-methyl-3-pentyl group.

Among these, a tert-butyl group is particularly desirable.

The term “aliphatic cyclic group” refers to a monocyclic group or polycyclic group that has no aromaticity.

In the “aliphatic cyclic group-containing acid dissociable group”, the “aliphatic cyclic group” may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

The basic ring of the “aliphatic cyclic group” exclusive of substituents is not limited to be constituted from only carbon and hydrogen (not limited to hydrocarbon groups), but is preferably a hydrocarbon group. Further, the “hydrocarbon group” may be either saturated or unsaturated, but is preferably saturated.

The aliphatic cyclic group may be either a monocyclic group or a polycyclic group.

The aliphatic cyclic group preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. As such aliphatic cyclic groups, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane which may or may not be substituted with a lower alkyl group, a fluorine atom or a fluorinated alkyl group, may be used. Specific examples of aliphatic cyclic hydrocarbon groups include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. In these aliphatic cyclic hydrocarbon groups, part of the carbon atoms constituting the ring may be replaced with an ethereal oxygen atom (—O—).

Examples of aliphatic cyclic group-containing acid dissociable groups include

(i) a monovalent aliphatic cyclic group in which a substituent (a group or an atom other than hydrogen) is bonded to the carbon atom on the ring skeleton to which an atom adjacent to the acid dissociable group (e.g., “—O—” within “—C(═O)—O— group”) is bonded to form a tertiary carbon atom (hereafter, this group is sometimes referred to as a “group having a tertiary carbon atom on the ring skeleton of a cyclic alkyl group”); and

(ii) a group which has a branched alkylene group containing a tertiary carbon atom, and a monovalent aliphatic cyclic group to which the tertiary carbon atom is bonded.

In the group (i), as the substituent bonded to the carbon atom to which an atom adjacent to the acid dissociable group on the ring skeleton of the aliphatic cyclic group, an alkyl group which may have a substituent can be mentioned. Examples of the alkyl group include the same groups as those represented by R¹⁴ in formulas (1-1) to (1-9) described later.

Specific examples of the group (i) include groups represented by general formulas (1-1) to (1-9) shown below.

Specific examples of the group (ii) include groups represented by general formulas (2-1) to (2-6) shown below.

In the formulas above, R¹⁴ represents an alkyl group which may have a substituent; and g represents an integer of 0 to 8.

In the formulas above, each of R¹⁵ and R¹⁶ independently represents an alkyl group.

In formulas (1-1) to (1-9), the alkyl group for R¹⁴ may be linear, branched or cyclic, and is preferably linear or branched.

The linear alkyl group preferably has 1 to 5 carbon atoms, more preferably 1 to 4, and still more preferably 1 or 2. Specific examples include a methyl group, an ethyl group, an n-propyl group, an n-butyl group and an n-pentyl group. Among these, a methyl group, an ethyl group or an n-butyl group is preferable, and a methyl group or an ethyl group is more preferable.

The branched alkyl group preferably has 3 to 10 carbon atoms, and more preferably 3 to 5. Specific examples of such branched alkyl groups include an isopropyl group, an isobutyl group, a tert-butyl group, an isopentyl group and a neopentyl group, and an isopropyl group is particularly desirable.

The linear or branched alkyl group may have a substituent. Examples of the substituent include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O), a cyano group and a carboxy group.

The cyclic alkyl group preferably has 3 to 10 carbon atoms, and more preferably 5 to 8. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane. Examples of the monocycloalkane include cyclopentane and cyclohexane.

Examples of polycycloalkanes include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane.

The cyclic alkyl group may have a substituent. Specifically, part or all of the hydrogen atoms constituting the alkyl group may be substituted with an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, an oxygen atom (═O), a cyano group, a carboxy group or the like, and part or all of the carbon atoms constituting the alkyl group may be substituted with a hetero atom such as an oxygen atom, a sulfur atom or a nitrogen atom.

g is preferably an integer of 0 to 3, more preferably 1 to 3, and still more preferably 1 or 2.

In formulas (2-1) to (2-6), as the alkyl group for R¹⁵ and R¹⁶, the same alkyl groups as those for R¹⁴ can be used.

In formulas (1-1) to (1-9) and (2-1) to (2-6), part of the carbon atoms constituting the ring may be replaced with an ethereal oxygen atom (—O—).

Further, in formulas (1-1) to (1-9) and (2-1) to (2-6), one or more of the hydrogen atoms bonded to the carbon atoms constituting the ring may be substituted with a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom and a fluorinated alkyl group.

An “acetal-type acid dissociable group” generally substitutes a hydrogen atom at the terminal of an OH-containing polar group such as a carboxy group or hydroxyl group, so as to be bonded with an oxygen atom. When acid is generated upon exposure, the generated acid acts to break the bond between the acetal-type acid dissociable group and the oxygen atom to which the acetal-type, acid dissociable group is bonded, thereby forming an OH-containing polar group such as a carboxy group or a hydroxy group.

Examples of acetal-type acid dissociable groups include groups represented by general formula (p1) shown below.

In the formula, R¹′ and R²′ each independently represent a hydrogen atom or an alkyl group of 1 to 5 carbon atoms; n represents an integer of 0 to 3; and Y represents an alkyl group of 1 to 5 carbon atoms or an aliphatic cyclic group.

In general formula (p1), n is preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 0.

In formula (p1), R¹′ and R²′ each independently represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms. The alkyl group of 1 to 5 carbon atoms for R¹′ and R²′ is the same as defined for the alkyl group of 1 to 5 carbon atoms for R, preferably a methyl group or an ethyl group, and most preferably a methyl group.

The alkyl group of 1 to 5 carbon atoms for Y is the same as defined for the alkyl group of 1 to 5 carbon atoms for R^(1′) and R²′.

The cyclic alkyl group for Y preferably has 4 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane which may or may not be substituted with a fluorine atom or a fluorinated alkyl group may be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane.

Further, R¹′ and Y may each independently represent an alkyl group of 1 to 5 carbon atoms, and the terminal of R¹′ may be bonded to the terminal of Y.

In such a case, the cyclic group formed by the bonding is preferably a 4- to 7-membered ring, and more preferably a 4- to 6-membered ring. Specific examples of the cyclic group include tetrahydropyranyl group and tetrahydrofuranyl group.

In the present invention, examples of the structural unit (a1) include a structural unit (a11) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid decomposable group which exhibits increased polarity by the action of acid; a structural unit (a12) derived from hydroxystyrene or a hydroxystyrene derivative in which at least a part of the hydrogen atom of the hydroxy group is protected with a substituent containing an acid decomposable group; and a structural unit (a13) derived from vinylbenzoic acid or a vinylbenzoic acid derivative in which at least a part of the hydrogen atom within —C(═O)—OH is protected with a substituent containing an acid decomposable group.

In the present descriptions and claims, the term “structural unit derived from an acrylate ester” refers to a structural unit which is formed by the cleavage of the ethylenic double bond of an acrylate ester.

An “acrylate ester” refers to a compound in which the terminal hydrogen atom of the carboxy group of acrylic acid (CH₂═CH—COOH) has been substituted with an organic group.

The acrylate ester may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent. The substituent that substitutes the hydrogen atom bonded to the carbon atom on the α-position is atom other than hydrogen or a group, and examples thereof include an alkyl group of 1 to 5 carbon atoms, a halogenated alkyl group of 1 to 5 carbon atoms and a hydroxyalkyl group of 1 to 5 carbon atoms. A carbon atom on the α-position of an acrylate ester refers to the carbon atom bonded to the carbonyl group, unless specified otherwise.

Hereafter, an acrylate ester having the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent is sometimes referred to as “α-substituted acrylate ester”. Further, acrylate esters and α-substituted acrylate esters are collectively referred to as “(α-substituted) acrylate ester”.

In the α-substituted acrylate ester, the alkyl group as the substituent on the α-position is preferably a linear or branched alkyl group, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group and a neopentyl group.

Specific examples of the halogenated alkyl group of 1 to 5 carbon atoms as the substituent on the α-position include groups in which part or all of the hydrogen atoms of the aforementioned “alkyl group of 1 to 5 carbon atoms as the substituent on the α-position” are substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

Specific examples of the hydroxyalkyl group of 1 to 5 carbon atoms as the substituent on the α-position include groups in which part or all of the hydrogen atoms of the aforementioned “alkyl group of 1 to 5 carbon atoms as the substituent on the α-position” are substituted with a hydroxy group.

It is preferable that a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms is bonded to the α-position of the α-substituted acrylate ester, a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl group of 1 to 5 carbon atoms is more preferable, and in terms of industrial availability, a hydrogen atom or a methyl group is the most desirable.

A “structural unit derived from hydroxystyrene or a hydroxystyrene derivative” refers to a structural unit that is formed by the cleavage of the ethylenic double bond of hydroxystyrene or a hydroxystyrene derivative.

The term “hydroxystyrene derivative” includes compounds in which the hydrogen atom at the α-position of hydroxystyrene has been substituted with another substituent such as an alkyl group or a halogenated alkyl group; and derivatives thereof.

Here, the α-position (carbon atom on the α-position) refers to the carbon atom having the benzene ring bonded thereto, unless specified otherwise.

A “structural unit derived from vinylbenzoic acid or a vinylbenzoic acid derivative” refers to a structural unit that is formed by the cleavage of the ethylenic double bond of vinylbenzoic acid or a vinylbenzoic acid derivative.

The term “vinylbenzoic acid derivative” includes compounds in which the hydrogen atom at the α-position of vinylbenzoic acid has been substituted with another substituent such as an alkyl group or a halogenated alkyl group; and derivatives thereof. Here, the α-position (carbon atom on the α-position) refers to the carbon atom having the benzene ring bonded thereto, unless specified otherwise.

Herebelow, the structural unit (a11), the structural unit (a12) and the structural unit (a13) will be described.

(Structural Unit (a11))

More specific examples of the structural unit (a11) include a structural unit represented by general formula (a11-0-1) shown below and a structural unit represented by general formula (a11-0-2) shown below.

In the formulae, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; X¹ represents an acid dissociable group; Y³″ represents a divalent linking group; and X² represents an acid dissociable group.

In general formula (a11-0-1), R is the same as defined for R¹ in the aforementioned formula (a0-1).

X¹ is not particularly limited as long as it is an acid dissociable group. Examples thereof include the aforementioned tertiary alkyl ester-type acid dissociable groups and acetal-type acid dissociable groups, and tertiary alkyl ester-type acid dissociable groups are preferable.

In general formula (a11-0-2), R is the same as defined above.

X² is the same as defined for X¹ in general formula (a11-0-1).

The divalent linking group for Y³″ is not particularly limited, and preferable examples thereof include a divalent hydrocarbon group which may have a substituent and a divalent linking group containing a hetero atom, which were explained above as examples of the divalent linking group for Y¹ and Y² in the aforementioned formula (a0-1).

Among these, as the divalent linking group for Y², a linear or branched alkylene group, a divalent alicyclic hydrocarbon group or a divalent linking group containing a hetero atom is particularly desirable. Among these, an alkylene group or a divalent linking group containing a hetero atom is more preferable.

Specific examples of the structural unit (a11) include structural units represented by general formulas (a1-1) to (a1-4) shown below.

In the formulas, R, R¹′, R²′, n, Y and Y³″ are the same as defined above; and X′ represents a tertiary alkyl ester-type acid dissociable group.

In the formulas, the tertiary alkyl ester-type acid dissociable group for X′ include the same tertiary alkyl ester-type acid dissociable groups as those described above.

As R¹′, R²′, n and Y are respectively the same as defined for R¹′, R²′, n and Y in general formula (p1) described above in connection with the “acetal-type acid dissociable group”.

As examples of Y³″, the same groups as those described above for Y³″ in general formula (a11-0-2) can be given.

Specific examples of structural units represented by general formula (a1-1) to (a1-4) are shown below.

In the formulae shown below, R^(α) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

In the present invention, it is particularly desirable that the structural unit (a11) include at least one member selected from the group consisting of structural units represented by general formulae (a11-0-11) to (a11-0-15) shown below and a structural unit represented by general formula (a11-0-2) shown below.

Among these examples, as the structural unit (a1), it is preferable to include at least one structural unit selected from the group consisting of structural units represented by general formulae (a11-0-11) to (a11-0-15) shown below, and it is more preferable to include at least one structural unit selected from the group consisting of structural units represented by general formulae (a11-0-11) to (a11-0-13) and (a11-0-15).

In the formulas, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R²¹ represents an alkyl group; R²² represents a group which forms an aliphatic monocyclic group with the carbon atom to which R²² is bonded; R²³ represents a branched alkyl group; R²⁴ represents a group which forms an aliphatic polycyclic group with the carbon atom to which R²⁴ is bonded; R²⁵ represents a linear alkyl group of 1 to 5 carbon atoms; R¹⁵ and R′⁶ each independently represents an alkyl group; Y³″ represents a divalent linking group; and X² an acid dissociable group.

In the formulae, R, Y³″ and X² are the same as defined above.

In general formula (a11-0-11), as the alkyl group for R²¹, the same alkyl groups as those described above for R¹⁴ in formulae (1-1) to (1-9) can be used, preferably a methyl group, an ethyl group, an isopropyl group or a cyclic alkyl group (preferably a polycyclic group).

As the aliphatic monocyclic group formed by R²² and the carbon atoms to which R²² is bonded, the same aliphatic cyclic groups as those described above for the aforementioned tertiary alkyl ester-type acid dissociable group and which are monocyclic can be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane. The monocycloalkane is preferably a 3- to 11-membered ring, more preferably a 3- to 8-membered ring, still more preferably a 4- to 6-membered ring, and most preferably a 5- or 6-membered ring.

The monocycloalkane may or may not have part of the carbon atoms constituting the ring replaced with an ether bond (—O—).

Further, the monocycloalkane may have a substituent such as an alkyl group of 1 to 5 carbon atoms, a fluorine atom or a fluorinated alkyl group of 1 to 5 carbon atoms.

As an examples of R²² constituting such an aliphatic cyclic group, an alkylene group which may have an ether bond (—O—) interposed between the carbon atoms can be given.

Specific examples of structural units represented by general formula (a11-0-11) include structural units represented by the aforementioned formulas (a11-0-16) to (a1-1-23), (a1-1-27), (a1-1-31) and (a1-1-37). Among these, a structural unit represented by general formula (a11-1-02) shown below which includes the structural units represented by the aforementioned formulas (a11-1-16), (a1-1-17), (a1-1-20) to (a1-1-23), (a1-1-27), (a1-1-31), (a1-1-32), (a1-1-33) and (a1-1-37) is preferable. Further, a structural unit represented by general formula (a11-1-02′) shown below is also preferable.

In the formulae, h represents an integer of 1 to 4, and preferably 1 or 2.

In the formulae, R and R²¹ are the same as defined above; and h represents an integer of 1 to 4.

In general formula (a11-0-12), as the branched alkyl group for R²³, the same alkyl groups as those described above for R¹⁴ which are branched can be used, and an isopropyl group is particularly desirable.

As the aliphatic polycyclic group formed by R²⁴ and the carbon atoms to which R²⁴ is bonded, the same aliphatic cyclic groups as those described above for the aforementioned tertiary alkyl ester-type acid dissociable group and which are polycyclic can be used.

Specific examples of structural units represented by general formula (a11-0-12) include structural units represented by the aforementioned formulas (a1-1-26) and (a1-1-28) to (a1-1-30).

As the structural unit (a11-0-12), a structural unit in which the aliphatic polycyclic group formed by R²⁴ and the carbon atom to which R²⁴ is bonded is a 2-adamantyl group is preferable, and a structural unit represented by the aforementioned formula (a11-1-26) is particularly desirable.

In general formula (a11-0-13), R and R²⁴ are the same as defined above.

As the linear alkyl group for R²⁵, the same linear alkyl groups as those described above for R¹⁴ in the aforementioned formulas (1-1) to (1-9) can be mentioned, and a methyl group or an ethyl group is particularly desirable.

Specific examples of structural units represented by general formula (a11-0-13) include structural units represented by the aforementioned formulas (a11-0-1), (a1-1-2) and (a1-1-7) to (a1-1-15) which were described above as specific examples of the structural unit represented by general formula (a1-1).

As the structural unit (a11-0-13), a structural unit in which the aliphatic polycyclic group formed by R²⁴ and the carbon atom to which R²⁴ is bonded is a 2-adamantyl group is preferable, and a structural unit represented by the aforementioned formula (a1-1-1) or (a1-1-2) is particularly desirable.

Further, a structural unit in which the aliphatic polycyclic group formed by R²⁴ and the carbon atom to which R²⁴ is bonded is a “group in which one or more hydrogen atoms have been removed from tetracyclododecane” is also preferable, and a structural unit represented by the aforementioned formula (a1-1-8), (a1-1-9) or (a1-1-30) is also preferable.

In general formula (a11-0-14), R and R²² are the same as defined above. R¹⁵ and R¹⁶ are the same as R¹⁵ and R¹⁶ in the aforementioned general formulae (2-1) to (2-6), respectively.

Specific examples of structural units represented by general formula (a11-0-14) include structural units represented by the aforementioned formulae (a1-1-35) and (a1-1-36) which were described above as specific examples of the structural unit represented by general formula (a1-1).

In general formula (a11-0-15), R and R²⁴ are the same as defined above. R¹⁵ and R¹⁶ are the same as R¹⁵ and R¹⁶ in the aforementioned general formulae (2-1) to (2-6), respectively.

Specific examples of structural units represented by general formula (a11-0-15) include structural units represented by the aforementioned formulae (a1-1-4) to (a1-1-6) and (a1-1-34) which were described above as specific examples of the structural unit represented by general formula (a1-1).

Examples of structural units represented by general formula (a11-0-2) include structural units represented by the aforementioned formulae (a1-3) and (a1-4), and a structural unit represented by formula (a1-3) is particularly desirable.

Examples of structural units represented by general formula (a11-0-2) include structural units represented by the aforementioned formulas (a1-1-26) and (a1-1-28) to (a1-1-30). Preferable examples of such structural units include a structural unit represented by general formula (a1-1-01) shown below, a structural unit represented by general formula (a1-1-02) shown below, and a structural unit represented by general formula (a1-1-03) shown below.

In the formulae, R is the same as defined above; R¹³ represents a hydrogen atom or a methyl group; R′⁴ represents an alkyl group; e represents an integer of 1 to 10; and n′ represents an integer of 0 to 3.

In the formula, R is as defined above; Y²′ and Y²″ each independently represents a divalent linking group; X′ represents an acid dissociable group; and w¹ represents an integer of 0 to 3.

In general formulas (a1-3-01) and (a1-3-02), R¹³ is preferably a hydrogen atom.

R¹⁴ is the same as defined for R¹⁴ in the aforementioned formulas (1-1) to (1-9)

e is preferably an integer of 1 to 8, more preferably an integer of 1 to 5, and most preferably 1 or 2.

n′ is preferably 1 or 2, and most preferably 2.

Specific examples of structural units represented by general formula (a1-3-01) include structural units represented by the aforementioned formulas (a1-3-25) and (a1-3-26).

Specific examples of structural units represented by general formula (a1-3-02) include structural units represented by the aforementioned formulas (a1-3-27) and (a1-3-28).

In general formula (a1-3-03), as the divalent linking group for Y²′ and Y²″, the same groups as those described above for Y¹ and Y² in general formula (a1-3) can be used.

As Y²′, a divalent hydrocarbon group which may have a substituent is preferable, a linear aliphatic hydrocarbon group is more preferable, and a linear alkylene group is still more preferable. Among linear alkylene groups, a linear alkylene group of 1 to 5 carbon atoms is preferable, and a methylene group or an ethylene group is particularly desirable.

As Y²″, a divalent hydrocarbon group which may have a substituent is preferable, a linear aliphatic hydrocarbon group is more preferable, and a linear alkylene group is still more preferable. Among linear alkylene groups, a linear alkylene group of 1 to 5 carbon atoms is preferable, and a methylene group or an ethylene group is particularly desirable.

As the acid dissociable group for X′, the same groups as those described above can be used. X′ is preferably a tertiary alkyl ester-type acid dissociable group, more preferably the aforementioned group (i) in which a substituent is bonded to the carbon atom to which an atom adjacent to the acid dissociable group is bonded to on the ring skeleton to form a tertiary carbon atom. Among these, a group represented by the aforementioned general formula (1-1) is particularly desirable.

w¹ represents an integer of 0 to 3, preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 1.

As the structural unit represented by general formula (a1-3-03), a structural unit represented by general formula (a1-3-03-1) or (a1-3-03-2) shown below is preferable, and a structural unit represented by general formula (a1-3-03-1) is particularly desirable.

In the formulas, R and R¹⁴ are the same as defined above; a′ represents an integer of 1 to 10; b′ represents an integer of 1 to 10; and t represents an integer of 0 to 3.

In general formulas (a1-3-03-1) and (a1-3-03-2), a′ is the same as defined above, preferably an integer of 1 to 8, more preferably 1 to 5, and most preferably 1 or 2.

b′ is the same as defined above, preferably an integer of 1 to 8, more preferably 1 to 5, and most preferably 1 or 2.

t is preferably an integer of 1 to 3, and most preferably 1 or 2.

Specific examples of structural units represented by general formula (a1-3-03-1) or (a1-3-03-2) include structural units represented by the aforementioned formulas (a1-3-29) to (a1-3-32).

Furthermore, as the structural unit (a11), a structural unit represented by general formula (a11-1-1) is also preferable.

In the formula, R is the same as defined above; OZ represents an acid decomposable group; b′ represents an integer of 0 to 2; c′, d′ and e′ each independently represents an integer of 0 to 3; and the plurality of e′ and Z may be the same or different from each other.

In general formula (a11-1-1), b′ represents an integer of 0 to 2, and preferably 0. c′ represents an integer of 0 to 3, preferably 0 or 1, and more preferably 0. d′ represents an integer of 0 to 3, preferably 0 or 1, and more preferably 1. e′ represents an integer of 0 to 3, preferably 0 or 1, and more preferably 0.

In general formula (a11-1-1), OZ represents an acid decomposable group.

As the acid decomposable group for OZ, an acid decomposable group which is decomposed to form a hydroxy group (—OH) is preferable, and examples thereof include (1) a group in which a hydroxy group is protected with an acetal-type acid dissociable group Z, and (2) a group in which Z has a tertiary ester-type acid dissociable group within the structure thereof, and is further decomposed by a decarboxylation reaction after the acid dissociation. Examples of the acetal-type acid dissociable group for Z include groups represented by the aforementioned formula (p1). Examples of the tertiary alkyl ester-type acid dissociable group for Z include groups in which a group represented by any one of the aforementioned formulae (1-1) to (1-9) and (2-1) to (2-6) os bonded to the oxygen atom of OZ via an ester bond (—C(═O)—O—).

(Structural Unit (a12), Structural Unit (a13))

In the present specification, the structural unit (a12) is a structural unit derived from hydroxystyrene or a derivative thereof in which at least a part of the hydrogen atom within the hydroxy group is protected with a substituent containing an acid decomposable group.

Further, the structural unit (a13) is a structural unit derived from vinylbenzoic acid or a derivative thereof in which at least a part of the hydrogen atom within —C(═O)—OH is protected with a substituent containing an acid decomposable group. In the structural unit (a12) and the structural unit (a13), as the substituent containing an acid decomposable group, the tertiary alkyl ester-type acid dissociable group and the acetal-type acid dissociable group described above for the structural unit (a11) can be given as preferable examples.

Preferable examples of the structural unit (a12) and the structural unit (a13) include structural units represented by general formulae (a12-1) to (a12-4) and (a13-1) shown below.

In formulae (a12-1) to (a12-4) and (a13-1), R is the same as defined above; R⁸⁸ represents a halogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; q represents an integer of 0 to 4; R¹′ is the same as defined above; n represents an integer of 0 to 3; W² represents an aliphatic cyclic group, an aromatic hydrocarbon group or an alkyl group of 1 to 5 carbon atoms; r represents an integer of 1 to 3; R⁴¹, R⁴² and R⁴³ each independently represents a linear or branched alkyl group; and X¹ represents an acid dissociable group.

In the formulae (a12-1) to (a12-4) and (a13-1), the bonding position of “—O—CHR¹′—O—(CH₂)_(n)—W”, “—O—C(O)—O—C(R⁴¹)(R⁴²)(R⁴³)”, “—O—C(O)—O—X¹”, “—O—(CH₂)_(r)—C(O)—O—X¹” and “—C(O)—O—X¹” on the phenyl group may be the o-position, the m-position or the p-position. In terms of the effects of the present invention, the p-position is most preferable.

R⁸⁸ represents a halogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms.

Examples of the halogen atom for R⁸⁸ include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

The alkyl group of 1 to 5 carbon atoms and the halogenated alkyl group of 1 to 5 carbon atoms for R⁸⁸ are the same as defined for the alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms for R, respectively.

When q is 1, the bonding position of R⁸⁸ may be any of the o-position, the m-position and the p-position.

When q is 2, a desired combination of the bonding positions can be used.

However, 1≦p+q≦5.

q represents an integer of 0 to 4, preferably 0 or 1, and most preferably 0 from an industrial viewpoint.

n is an integer of 0 to 3, preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 1.

The aliphatic cyclic group for W² is a monovalent aliphatic cyclic group. The aliphatic cyclic group can be selected appropriately, for example, from the multitude of groups that have been proposed for conventional ArF resists. Specific examples of the aliphatic cyclic group include an aliphatic monocyclic group of 5 to 7 carbon atoms and an aliphatic polycyclic group of 10 to 16 carbon atoms.

The aliphatic cyclic group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

The basic ring of the “aliphatic cyclic group” exclusive of substituents is not limited to be constituted from only carbon and hydrogen (not limited to hydrocarbon groups), and may have an oxygen atom or the like in the ring structure thereof.

As the aliphatic monocyclic group of 5 to 7 carbon atoms, a group in which one hydrogen atom has been removed from a monocycloalkane can be mentioned, and specific examples include a group in which one hydrogen atom has been removed from cyclopentane or cyclohexane.

Examples of the aliphatic polycyclic group of 10 to 16 carbon atoms include groups in which one hydrogen atom has been removed from a bicycloalkane, tricycloalkane, tetracycloalkane or the like. Specific examples include groups in which one hydrogen atom has been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Of these, an adamantyl group, a norbornyl group and a tetracyclododecyl group is preferred industrially, and an adamantyl group is particularly desirable.

As the aromatic cyclic hydrocarbon group for W², aromatic polycyclic groups of 10 to 16 carbon atoms can be mentioned. Examples of such aromatic polycyclic groups include groups in which one hydrogen atom has been removed from naphthalene, anthracene, phenanthrene or pyrene. Specific examples include a 1-naphthyl group, a 2-naphthyl group, a 1-anthryl group, a 2-anthryl group, a 1-phenanthryl group, a 2-phenanthryl group, a 3-phenanthryl group and a 1-pyrenyl group, and a 2-naphthyl group is preferred industrially.

The alkyl group of 1 to 5 carbon atoms for W² is the same as defined for the alkyl group of 1 to 5 carbon atoms which may be bonded to the α-position of hydroxystyrene, preferably a methyl group or an ethyl group, and most preferably an ethyl group.

Each of R⁴¹ to R⁴³ is preferably an alkyl group of 1 to 5 carbon atoms, and more preferably an alkyl group of 1 to 3 carbon atoms. Specific examples thereof are the same as defined for the alkyl group of 1 to 5 carbon atoms for R.

The acid dissociable group for X¹ is the same as defined for the acid dissociable group for X¹ in the aforementioned formula (a11-0-1).

r is preferably 1 or 2, and more preferably 1.

Among the structural unit (a12) and the structural unit (a13), the structural unit (a12) is preferable, and a structural unit represented by general formula (a12-1) or a structural unit represented by general formula (a12-4) is more preferable.

Specific examples of preferable structural units (a12) are shown below.

As the structural unit (a12), at least one member selected from chemical formulae (a12-1-1) to (a12-1-12) is preferable, and any one of chemical formula (a12-1-1), (a12-1-2) and (a12-1-5) to (a12-1-12) is most preferable.

As the structural unit (a1) contained in the component (A1), 1 type of structural unit may be used, or 2 or more types may be used.

As the structural unit (a1), a structural unit (a11) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent is preferable.

In the component (A1), the amount of the structural unit (a1) based on the combined total of all structural units constituting the component (A1) is preferably 10 to 80 mol %, more preferably 15 to 75 mol %, still more preferably 20 to 70 mol %, and most preferably 25 to 65 mol %.

When the amount of the structural unit (a1) is at least as large as the lower limit of the above-mentioned range, a pattern can be easily formed using a resist composition prepared from the component (A1), and various lithography properties such as sensitivity, resolution, LWR and the like are improved. On the other hand, when the amount of the structural unit (a1) is no more than the upper limit of the above-mentioned range, a good balance can be reliably achieved with the other structural units.

(Other structural units)

The component (A1) may also have a structural unit other than the above-mentioned structural units (a0) and (a1), as long as the effects of the present invention are not impaired.

As such a structural unit, any other structural unit which cannot be classified as the aforementioned structural units can be used without any particular limitation, and any of the multitude of conventional structural units used within resist resins for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used.

Examples of the other structural unit include a structural unit (a2) containing a lactone-containing cyclic group, a structural unit (a3) containing a polar group-containing group (provided that structural units which fall under the definition of the structural units (a0) or (a1) are excluded), and a structural unit (a4) containing an acid non-dissociable aliphatic polycyclic group.

Structural Unit (a2)

The component (A1) preferably includes a structural unit (a2) containing a lactone-containing cyclic group, as well as the structural units (a0) and (a1).

When the component (A1) is used for forming a resist film, the structural unit (a2) containing a lactone-containing cyclic group is effective in improving the adhesion between the resist film and the substrate. Further, in an alkali developing process, the structural unit (a2) is effective in terms of improving the affinity for a water-containing developing solution such as an alkali developing solution.

The aforementioned structural unit (a0) or (a1)) which contains a lactone-containing cyclic group falls under the definition of the structural unit (a2); however, such a structural unit is regarded as a structural unit (a0) or (a1), and does not fall under the definition of the structural unit (a2).

The term “lactone ring-containing group” refers to a cyclic group including a ring containing a —O—C(═O)— structure (lactone ring). The term “lactone ring” refers to a single ring containing a —O—C(O)— structure, and this ring is counted as the first ring. A lactone-containing cyclic group in which the only ring structure is the lactone ring is referred to as a monocyclic group, and groups containing other ring structures are described as polycyclic groups regardless of the structure of the other rings. The lactone-containing cyclic group may be either a monocyclic group or a polycyclic group.

The lactone-containing cyclic group for the structural unit (a2) is not particularly limited, and an arbitrary structural unit may be used. Specific examples of lactone-containing monocyclic groups include a group in which one hydrogen atom has been removed from a 4- to 6-membered lactone ring, such as a group in which one hydrogen atom has been removed from β-propionolatone, a group in which one hydrogen atom has been removed from γ-butyrolactone, and a group in which one hydrogen atom has been removed from δ-valerolactone. Further, specific examples of lactone-containing polycyclic groups include groups in which one hydrogen atom has been removed from a lactone ring-containing bicycloalkane, tricycloalkane or tetracycloalkane.

Specific examples include groups represented by general formulae (a2-2-1) to (a2-2-7) shown below.

In the formulas, R′ independently represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, —COOR″, OC(═O)R″, a hydroxyalkyl group or a cyano group, wherein R″ represents a hydrogen atom or an alkyl group; s″ represents an integer of 0 to 2; A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; and m represents 0 or 1.

The alkyl group for R′ is preferably an alkyl group of 1 to 6 carbon atoms. Further, the alkyl group is preferably a linear alkyl group or a branched alkyl group. Specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group and a hexyl group. Among these, a methyl group or ethyl group is preferable, and a methyl group is particularly desirable.

As the alkoxy group, an alkoxy group of 1 to 6 carbon atoms is preferable.

Further, the alkoxy group is preferably a linear or branched alkoxy group. Specific examples of the alkoxy group include the aforementioned alkyl groups for the substituent having an oxygen atom (—O—) bonded thereto.

Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

As examples of the halogenated alkyl group, groups in which part or all of the hydrogen atoms of the aforementioned alkyl groups for the substituent have been substituted with the aforementioned halogen atoms can be given. As the halogenated alkyl group, a fluorinated alkyl group is preferable, and a perfluoroalkyl group is particularly desirable.

In the —COOK″ group and the —OC(═O)R″ group, R″ represents a hydrogen atom or a linear, branched or cyclic alkyl group of 1 to 15 carbon atoms.

When R″ represents a linear or branched alkyl group, it is preferably an alkyl group of 1 to 10 carbon atoms, more preferably an alkyl group of 1 to 5 carbon atoms, and most preferably a methyl group or an ethyl group.

When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

The hydroxyalkyl group preferably has 1 to 6 carbon atoms, and specific examples thereof include the aforementioned alkyl groups for the substituent in which at least one hydrogen atom has been substituted with a hydroxy group.

A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom, preferably an alkylene group of 1 to 5 carbon atoms, an oxygen atom (—O—) or a sulfur atom (—S—), and more preferably an alkylene group of 1 to 5 carbon atoms or —O—. The alkylene group of 1 to 5 carbon atoms is preferably a methylene group or a dimethylmethylene group, and most preferably a methylene group. As the alkylene group of 1 to 5 carbon atoms, a methylene group or a dimethylethylene group is preferable, and a methylene group is particularly desirable.

Specific examples of groups represented by general formulae a2-2-1) to (a2-2-7) are shown below.

More specifically, examples of the structural unit (a2) include structural units represented by general formula (a2-0) shown below.

In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R²⁸ represents a lactone ring-containing group; and R²⁹ represents a single bond or a divalent linking group.

In general formula (a2-0), R is the same as defined above.

R²⁸ is the same as defined for the aforementioned lactone-ring containing group.

R²⁹ may be either a single bond or a divalent linking group. In terms of the effects of the present invention, a divalent linking group is preferable.

The divalent linking group for R²⁹ is not particularly limited, and examples thereof include the same divalent linking groups as those described above for Y¹ or Y² in the aforementioned formula (a0-1). Among these, an alkylene group or a divalent linking group containing an ester bond (—C(═O)—O—) is preferable.

As the alkylene group, a linear or branched alkylene group is preferable. Specific examples include the same linear alkylene groups and branched alkylene groups as those described above for the aliphatic hydrocarbon group represented by Y².

As the divalent linking group containing an ester bond, a group represented by general formula: —R³⁰—C(═O)—O— (in the formula, R³⁰ represents a divalent linking group) is particularly desirable. That is, the structural unit (a2^(S)) is preferably a structural unit represented by general formula (a2-0-1) shown below.

In the formula, R and R²⁸ are the same as defined above; and R³⁰ represents a divalent linking group.

R³⁰ is not particularly limited, and examples thereof include the same divalent linking groups as those described above for Y¹ and Y² in the aforementioned formula (a0-1).

As the divalent linking group for R³⁰, a linear or branched alkylene group, an aliphatic hydrocarbon group having a ring in the structure thereof, or a divalent linking group containing a hetero atom is preferable, and a linear or branched alkylene group or a divalent linking group containing a hetero atom is more preferable.

As the linear alkylene group, a methylene group or an ethylene group is preferable, and a methylene group is particularly desirable.

As the branched alkylene group, an alkylmethylene group or an alkylethylene group is preferable, and —CH(CH₃)—, —C(CH₃)₂— or —C(CH₃)₂CH₂— is particularly desirable.

As the divalent linking group containing an oxygen atom, a divalent linking group containing an ether bond or an ester bond is preferable.

As the structural unit (a2) contained in the component (A1), 1 type of structural unit may be used, or 2 or more types may be used.

When the component (A1) contains the structural unit (a2), the amount of the structural unit (a2) based on the combined total of all structural units constituting the component (A1) is preferably 1 to 80 mol %, more preferably 10 to 70 mol %, still more preferably 10 to 65 mol %, and most preferably 10 to 60 mol %. When the amount of the structural unit (a2) is at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a2) can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a2) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units, and various lithography properties such as DOF and CDU and pattern shape can be improved.

Structural Unit (a3)

The structural unit (a3) is a structural unit containing a polar group, which does not fall under the definition of the aforementioned structural units (a0) and (a1). When the component (A1) includes the structural unit (a3), the polarity of the component (A1) after exposure is further increased. Increase in the polarity contributes to improvement in terms of resolution and the like, particularly in an alkali developing process.

Examples of the polar group include —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂. Structural units that contain —COOH include structural units of (α-substituted) acrylic acid.

The structural unit (a3) is preferably a structural unit containing a hydrocarbon group in which part of the hydrogen atoms has been substituted with a polar group. The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Among these, as the hydrocarbon group, an aliphatic hydrocarbon group is preferable.

Examples of the aliphatic hydrocarbon group as the hydrocarbon group include linear or branched hydrocarbon groups (preferably alkylene groups) of 1 to 10 carbon atoms, and aliphatic cyclic groups (monocyclic groups and polycyclic groups).

These aliphatic cyclic groups (monocyclic groups and polycyclic groups) can be selected appropriately from the multitude of groups that have been proposed for the resins of resist compositions designed for use with ArF excimer lasers. The aliphatic cyclic group preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. As the aliphatic cyclic group, a group in which two or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane can be used. Specific examples include groups in which two or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which two or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. The aliphatic cyclic group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, and a fluorinated alkyl group of 1 to 5 carbon atoms.

The aromatic hydrocarbon group for the hydrocarbon group is a hydrocarbon group having an aromatic ring, and preferably has 5 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, still more preferably 6 to 15 carbon atoms, and most preferably 6 to 10 carbon atoms. Here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the aromatic hydrocarbon group. The aromatic ring included in the aromatic hydrocarbon group is the same as defined above, and specific examples include benzene, naphthalene, anthracene and phenanthrene.

Specific examples of the aromatic hydrocarbon group include a group in which two hydrogen atoms have been removed from the aforementioned aromatic ring (arylene group); a group in which two hydrogen atoms have been removed from an aromatic compound having two or more aromatic rings (biphenyl, fluorene or the like); and a group in which one hydrogen atom of the aforementioned aromatic hydrocarbon ring has been substituted with an alkylene group (a group in which one hydrogen atom has been removed from the aryl group within the aforementioned arylalkyl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group, or a 2-naphthylethyl group). The alkylene group (alkyl chain within the arylalkyl group) preferably has 1 to 4 carbon atom, more preferably 1 or 2, and most preferably 1.

The aromatic hydrocarbon group may or may not have a substituent. For example, the hydrogen atom bonded to the aromatic ring within the aromatic hydrocarbon group may be substituted with a substituent. Examples of the substituent include an alkyl group, a halogen atom and a halogenated alkyl group.

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

Examples of the halogen atom as the substituent for the aromatic hydrocarbon group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms.

As the structural unit (a3), a structural unit represented by general formula (a3-1) shown below is preferable.

In the formulae, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; P⁰ represents —C(═O)—O—, —C(═O)—NR⁰— (wherein R⁰ represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms) or a single bond; and W⁰ represents —COOH, a hydrocarbon group having at least one substituent selected from the group consisting of —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂, or —CONHCO—R^(a3) (R^(a3) represents a hydrocarbon group), provided that the hydrocarbon group may have an oxygen atom or a sulfur atom at an arbitrary position.

In the formula (a3-1), R is the same as defined above.

In the formula (a3-1), P⁰ represents —C(═O)—O—, —C(═O)—NR⁰— (wherein R⁰ represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms) or a single bond. The alkyl group for R⁰ is the same as defined for the alkyl group for R.

In the formula (a3-1), W⁰ represents a hydrocarbon group having at least one substituent selected from the group consisting of —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂, or —CONHCO—R^(a3) (R^(a3) represents a hydrocarbon group), provided that the hydrocarbon group may have an oxygen atom or a sulfur atom at an arbitrary position.

A “hydrocarbon group which has a substituent” refers to a hydrocarbon group in which at least part of the hydrogen atoms bonded to the hydrocarbon group is substituted with a substituent.

The hydrocarbon group for W⁰ or R^(a3) may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group.

Preferable examples of the aliphatic hydrocarbon group for W⁰ or R^(a3) include linear or branched hydrocarbon groups of 1 to 10 carbon atoms (preferably alkylene groups) and aliphatic cyclic groups (monocyclic groups and polycyclic groups), and are the same as explained above.

The aromatic hydrocarbon group for W⁰ or R^(a3) is a hydrocarbon group having at least one aromatic ring, and is the same as explained above.

W⁰ may have an oxygen atom or a sulfur atom at an arbitrary position. Here, the expression “may have an oxygen atom or a sulfur atom at an arbitrary position” means that part of the carbon atoms constituting the hydrocarbon group or the hydrocarbon group having a substituent (including the carbon atoms of the substituent part) may be substituted with an oxygen atom or a sulfur atom, or a hydrogen atom bonded to the hydrocarbon group may be substituted with an oxygen atom or a sulfur atom.

Examples of W⁰ which has an oxygen atom (O) at an arbitrary position are shown below.

In the formulae, w represents a hydrocarbon group; and R^(m) represents an alkylene group of 1 to 5 carbon atoms.

In the formulae above, W⁰⁰ represents a hydrocarbon group, and is the same as defined for W⁰ in the aforementioned formula (a3-1). W⁰⁰ is preferably an aliphatic hydrocarbon group, and more preferably an aliphatic cyclic group (a monocyclic group or a polycyclic group).

R^(m) is preferably linear or branched, preferably an alkylene group of 1 to 3 carbon atoms, and more preferably a methylene group or an ethylene group.

Specific examples of preferable structural units as the structural unit (a3) include a structural unit derived from an (α-substituted) acrylate ester, and structural units represented by general formulae (a3-11) to (a3-13) shown below. Examples of the structural unit derived from an (α-substituted) acrylate ester include a structural unit in which P⁰ in the aforementioned formula (a3-1) is a single bond and W⁰ is —COOH.

In the formulae, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W⁰¹ represents an aromatic hydrocarbon group which has at least one substituent selected from the group consisting of —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂; each of P⁰² and P⁰³ independently represents —C(═O)—O—, —C(═O)—NR⁰— (wherein R⁰ represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms) or a single bond; W⁰² represents a cyclic hydrocarbon group having at least one substituent selected from the group consisting of —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂, or —CONHCO—R^(a32) (R^(a32) represents a cyclic hydrocarbon group), provided that the hydrocarbon group may have an oxygen atom or a sulfur atom at an arbitrary position; and W⁰³ represents a chain-like hydrocarbon group having at least one substituent selected from the group consisting of —OH, —COOH, —CN, —SO₂NH₂ and —CONH₂, or —CONHCO—R^(a33) (R^(a33) represents a chain-like alkyl group).

[Structural Unit Represented by General Formula (a3-11)]

In the formula (a3-11), R is the same as defined for R in the aforementioned formula (a3-1).

The aromatic hydrocarbon group for W⁰¹ is the same as defined for the aromatic hydrocarbon group for W⁰ in the aforementioned formula (a3-1).

Specific examples of structural units preferable as a structural unit represented by general formula (a3-11) are shown below. In the formulae shown below, R^(α) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

[Structural Unit Represented by General Formula (a3-12)]

In the formula (a3-12), R is the same as defined for R in the aforementioned formula (a3-1).

P⁰² represents —C(═O)—O—, —C(═O)—NR⁰— (wherein R⁰ represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms) or a single bond, and is preferably —C(═O)—O— or a single bond. The alkyl group for R⁰ is the same as defined for the alkyl group for R.

The cyclic hydrocarbon group for W⁰² or R^(a32) is the same as defined for the aliphatic cyclic groups (monocyclic groups and polycyclic groups) and aromatic hydrocarbon groups explained above for W⁰ in the aforementioned formula (a3-1).

W⁰² or R^(a32) may have an oxygen atom or a sulfur atom at an arbitrary position, and is the same as defined for W⁰ in the aforementioned formula (a3-1).

Specific examples of structural units preferable as a structural unit represented by general formula (a3-12) are shown below. In the formulae shown below, R^(α) represents a hydrogen atom, a methyl group or a trifluoromethyl group.

When the component (A1) includes a structural unit (a3), as the structural unit (a3), one type of structural unit may be used, or two or more types may be used.

When the component (A1) contains the structural unit (a3), the amount of the structural unit (a3) based on the combined total of all structural units constituting the component (A1) is preferably 0 to 85 mol %, and more preferably 0 to 80 mol %. When the amount of the structural unit (a3) is at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a3) (effect of improving resolution, lithography properties and pattern shape) can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a3) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

Structural Unit (a4)

The structural unit (a4) is a structural unit containing a non-acid dissociable, aliphatic polycyclic group.

In the structural unit (a4), examples of this polycyclic group include the same polycyclic groups as those described above in relation to the aforementioned structural unit (a1), and any of the multitude of conventional polycyclic groups used within the resin component of resist compositions for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used.

In consideration of industrial availability and the like, at least one polycyclic group selected from amongst a tricyclodecyl group, adamantyl group, tetracyclododecyl group, isobornyl group, and norbornyl group is particularly desirable. These polycyclic groups may be substituted with a linear or branched alkyl group of 1 to 5 carbon atoms.

Specific examples of the structural unit (a4) include units with structures represented by general formulas (a4-1) to (a4-5) shown below.

In the formulae, R is the same as defined above.

When the structural unit (a4) is included in the component (A1), the amount of the structural unit (a4) based on the combined total of all the structural units that constitute the component (A1) is preferably within the range from 1 to 30 mol %, and more preferably from 10 to 20 mol %.

In the resist composition of the present invention, the component (A) contains a polymeric compound (A1) having the aforementioned structural units (a0) and (a1).

Specific examples of the component (A 1) include a polymeric compound consisting of a structural unit (a0), a structural unit (a1) and a structural unit (a2); a polymeric compound consisting of a structural unit (a0), a structural unit (a1) and a structural unit (a3); a polymeric compound consisting of a structural unit (a0), a structural unit (a1), a structural unit (a2) and a structural unit (a3); and a polymeric compound consisting of a structural unit (a0), a structural unit (a1), a structural unit (a2), a structural unit (a3) and a structural unit (a4).

In the component (A), as the component (A1), one type may be used alone, or two or more types may be used in combination.

In the component (A), the amount of the component (A1) based on the total weight of the component (A) is preferably 25% by weight or more, more preferably 50% by weight or more, still more preferably 75% by weight or more, and most preferably 100% by weight. When the amount of the component (A1) is 25% by weight or more, the effects of the present invention are further improved.

The weight average molecular weight (Mw) (the polystyrene equivalent value determined by gel permeation chromatography) of the component (A1) is not particularly limited, but is preferably 1,000 to 50,000, more preferably 1,500 to 30,000, and most preferably 2,000 to 20,000. When the weight average molecular weight is no more than the upper limit of the above-mentioned range, the resist composition exhibits a satisfactory solubility in a resist solvent. On the other hand, when the weight average molecular weight is at least as large as the lower limit of the above-mentioned range, dry etching resistance and the cross-sectional shape of the resist pattern becomes satisfactory.

Further, the dispersity (Mw/Mn) is not particularly limited, but is preferably 1.0 to 5.0, more preferably 1.0 to 3.0, and most preferably 1.0 to 2.5. Here, Mn is the number average molecular weight.

The component (A) can be obtained, for example, by a conventional radical polymerization or the like of the monomers corresponding with each of the structural units, using a radical polymerization initiator such as azobisisobutyronitrile (AIBN).

Furthermore, in the component (A), by using a chain transfer agent such as HS—CH₂—CH₂—CH₂—C(CF₃)₂—OH, a —C(CF₃)₂—OH group can be introduced at the terminals of the component (A1). Such a copolymer having introduced a hydroxyalkyl group in which some of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is effective in reducing developing defects and LER (line edge roughness: unevenness of the side walls of a line pattern).

As the monomers which yield the corresponding structural units, commercially available monomers may be used, or the monomers may be synthesized by a conventional method.

The component (A) may contain a base component other than the component (A1) (hereafter, such base component is referred to as “component (A2)”), as long as the effects of the present invention are not impaired.

As the component (A2) a low molecular weight compound that have a molecular weight of at least 500 and less than 4,000, contains a hydrophilic group, and also contains an acid dissociable group described above in connection with the component (A1), can be used. Specific examples include compounds containing a plurality of phenol skeletons in which part or all of the hydrogen atoms within hydroxyl groups have been substituted with the aforementioned acid dissociable groups.

Examples of the low-molecular weight compound include low molecular weight phenolic compounds in which a portion of the hydroxyl group hydrogen atoms have been substituted with an aforementioned acid dissociable group, and these types of compounds are known, for example, as sensitizers or heat resistance improvers for use in non-chemically amplified g-line or i-line resists.

Examples of these low molecular weight phenol compounds include bis(4-hydroxyphenyl)methane, bis(2,3,4-trihydroxyphenyl)methane, 2-(4-hydroxyphenyl)-2-(4′-hydroxyphenyl)propane, 2-(2,3,4-trihydroxyphenyl)-2-(2,3′,4′-trihydroxyphenyl)propane, tris(4-hydroxyphenyl)methane, bis(4-hydroxy-3,5-dimethylphenyl)-2-hydroxyphenylmethane, bis(4-hydroxy-2,5-dimethylphenyl)-2-hydroxyphenylmethane, bis(4-hydroxy-3,5-dimethylphenyl)-3,4-dihydroxyphenylmethane, bis(4-hydroxy-2,5-dimethylphenyl)-3,4-dihydroxyphenylmethane, bis(4-hydroxy-3-methylphenyl)-3,4-dihydroxyphenylmethane, bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-4-hydroxyphenylmethane, bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-3,4-dihydroxyphenylmethane, 1-[1-(4-hydroxyphenyl)isopropyl]-4-[1,1-bis(4-hydroxyphenyl)ethyl]benzene, and dimers, trimers, tetramers, pentamers and hexamers of formalin condensation products of phenols such as phenol, m-cresol, p-cresol and xylenol. Needless to say, the low molecular weight phenol compound is not limited to these examples. In particular, a phenol compound having 2 to 6 triphenylmethane skeletons is preferable in terms of resolution and line edge roughness (LER). Also, there are no particular limitations on the acid dissociable group, and suitable examples include the groups described above.

In the resist composition of the present invention, the amount of the component (A) can be appropriately adjusted depending on the thickness of the resist film to be formed, and the like.

<Acid Generator Component; Component (B)>

The component (B) is an acid generator component which generates acid upon exposure.

As the component (B), there is no particular limitation, and any of the known acid generators used in conventional chemically amplified resist compositions can be used. Examples of these acid generators are numerous, and include onium salt acid generators such as iodonium salts and sulfonium salts; oxime sulfonate acid generators; diazomethane acid generators such as bisalkyl or bisaryl sulfonyl diazomethanes and poly(bis-sulfonyl)diazomethanes; nitrobenzylsulfonate acid generators; iminosulfonate acid generators; and disulfone acid generators.

As an onium salt acid generator, a compound represented by general formula (b-1) or (b-2) shown below can be used.

In the formulae, R¹⁰¹ represents a cyclic group which may have a substituent, a linear alkyl group which may have a substituent or a linear alkenyl group which may have a substituent; Y¹⁰¹ represents a single bond or a divalent linking group containing an oxygen atom; V¹⁰¹ represents a single bond, an alkylene group or a fluorinated alkylene group; R¹⁰² represents a fluorine atom or a fluorinated alkyl group of 1 to 5 carbon atoms; R¹⁰⁴ and R¹⁰⁵ each independently represents an alkyl group of 1 to 10 carbon atoms or a fluorinated alkyl group of 1 to 10 carbon atoms, provided that R¹⁰⁴ and R¹⁰⁵ may be mutually bonded to form a ring; and M^(m+) represents an organic cation having a valency of m.

{Anion Moiety}

The cyclic group for R¹⁰¹ which may have a substituent may be a cyclic aliphatic hydrocarbon group (aliphatic cyclic group), an aromatic hydrocarbon group (aromatic cyclic group) or a hetero ring which contains a hetero atom in the ring thereof.

Examples of the cyclic aliphatic hydrocarbon group for R¹⁰¹ include groups in which one hydrogen atom has been removed from a monocycloalkane or a polycycloalkane described above for the divalent aliphatic hydrocarbon group, and an adamantyl group or a norbornyl group is preferable.

Examples of the aromatic hydrocarbon group for R¹⁰¹ include the aromatic hydrocarbon rings described above for the divalent aromatic hydrocarbon group, and an aryl group in which one hydrogen atom has been removed from an aromatic compound having two or more aromatic rings, and a phenyl group or a naphthyl group is preferable.

Specific examples of the hetero ring for R¹⁰¹ include groups represented by formulae (L1) to (L6) and (S1) to (S4) shown below.

In the formula, Q″ represents an alkylene group of 1 to 5 carbon atoms, —O—, —S—, —O—R⁹⁴— or —S—R⁹⁵— (wherein each of R⁹⁴ and R⁹⁵ independently represents an alkylene group of 1 to 5 carbon atoms); and m represents 0 or 1.

In the formulae, the alkylene group for Q″, R⁹⁴ and R⁹⁵ is preferably a methylene group.

Examples of the hetero ring for R¹⁰¹ mother than those described above include the following.

The cyclic aliphatic hydrocarbon group, aromatic hydrocarbon group or hetero ring for R¹⁰¹ may have a substituent. Here, the hydrocarbon ring or the hetero ring “has a substituent” means that part or all of the hydrogen atoms bonded to the ring structure of the hydrocarbon ring or the hetero ring has been substituted with an atom or a group other than hydrogen. Examples of the substituent include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) and a nitro group.

The alkyl group as the substituent is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable.

The alkoxy group as the substituent is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group.

Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable.

Example of the halogenated alkyl group as the substituent for the aforementioned aromatic hydrocarbon group include groups in which part or all of the hydrogen atoms within an alkyl group of 1 to 5 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group) have been substituted with the aforementioned halogen atoms.

The chain-like alkyl group for R¹⁰¹ may be linear or branched.

The linear alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 10. Specific examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, an isotridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group and a docosyl group.

The branched alkyl group preferably has 3 to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to 10. Specific examples include a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group.

The alkenyl group for R¹⁰¹ preferably has 2 to 10 carbon atoms, more preferably 2 to 5, still more preferably 2 to 4, and most preferably 3. Examples thereof include a vinyl group, a propenyl group (an allyl group) and a butynyl group. Among these, a propenyl group is particularly desirable.

Examples of the substituent for the chain-like alkyl group or alkenyl group represented by R¹⁰¹ include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O), a nitro group (which are the same as defined for the substituent for the aforementioned cyclic group), and the aforementioned cyclic group.

In the present invention, as R¹⁰¹, a cyclic group which may have a substituent is preferable, and a phenyl group, a naphthyl group, a group in which one or more hydrogen atoms have been removed from a polycycloalkane, and a lactone-containing cyclic group or an —SO₂— containing cyclic group represented by the aforementioned formula (L1) to (L6) and (51) to (S4).

The divalent linking group containing an oxygen atom for Y¹⁰¹ may contain an atom other than an oxygen atom. Examples of atoms other than oxygen include a carbon atom, a hydrogen atom, a sulfur atom and a nitrogen atom.

Examples of divalent linking groups containing an oxygen atom include non-hydrocarbon, oxygen atom-containing linking groups such as an oxygen atom (an ether bond; —O—), an ester bond (—C(═O)—O—), an amido bond (—C(═O)—NH—), a carbonyl group (—C(═O)—) and a carbonate bond (—O—C(═O)—O—); and combinations of the aforementioned non-hydrocarbon, hetero atom-containing linking groups with an alkylene group. Furthermore, the combinations may have a sulfonyl group (—SO₂—) bonded thereto.

Specific examples of such combinations include —V¹⁰⁵—O—, —V¹⁰⁵—O—C(═O)—, —C(═O)—O—V¹⁰⁵—O—C(═O), —SO₂—O—V¹⁰⁵ and —V¹⁰⁵—SO₂—O—V¹⁰⁶—O—C(═O)— (in the formula, V¹⁰⁵ and V¹⁰⁶ each independently represents an alkylene group).

The alkylene group for V¹⁰⁵ and V¹⁰⁶ is preferably a linear or branched alkylene group, and preferably has 1 to 12 carbon atoms, more preferably 1 to 5, and most preferably 1 to 3.

The alkylene group is the same as defined for the alkylene group for Y¹ and Y².

As Q′, a divalent linking group containing an ester bond or an ether bond is preferable, and —V¹⁰⁵—O—, —V¹⁰⁵—O—C(═O)— or —C(═O)—O—V¹⁰⁵—O—C(═O)— is more preferable.

The alkylene group for V¹⁰¹ is the same as defined for Y¹ and Y², preferably has 1 to 5 carbon atoms.

Examples of the fluorinated alkyl group for V¹⁰¹ include groups in which part or all of the hydrogen atoms constituting the alkylene group for Y¹ and Y² has been substituted with a fluorine atom. The number of carbon atoms is preferably 1 to 5, and more preferably 1 or 2.

Examples of the fluorinated alkyl group of 1 to 5 carbon atoms for R¹⁰² include groups in which part or all of the hydrogen atoms constituting an alkyl group of 1 to 5 carbon atoms have been substituted with a fluorine atom.

R¹⁰⁴ and R¹⁰⁵ each independently represents an alkyl group of 1 to 10 carbon atoms or a fluorinated alkyl group of 1 to 10 carbon atoms, provided that R¹⁰⁴ and R¹⁰⁵ may be mutually bonded to form a ring.

Each of R¹⁰⁴ and R¹⁰⁵ is preferably a linear or branched (fluorinated) alkyl group. The (fluorinated) alkyl group preferably has 1 to 10 carbon atoms, preferably 1 to 7, and more preferably 1 to 3. The smaller the number of carbon atoms of the (fluorinated) alkyl group for R¹⁰⁴ and R¹⁰⁵, the more the solubility in a resist solvent is improved.

Further, in the (fluorinated) alkyl group for R¹⁰⁴ and R¹⁰⁵, it is preferable that the number of hydrogen atoms substituted with fluorine atoms is as large as possible because the acid strength increases and the transparency to high energy radiation of 200 nm or less or electron beam is improved.

The fluorination ratio of the (fluorinated) alkyl group is preferably from 70 to 100%, more preferably from 90 to 100%, and it is particularly desirable that the alkylene group or alkyl group be a perfluoroalkylene group or perfluoroalkyl group in which all hydrogen atoms are substituted with fluorine atoms.

Specific examples of the anion represented by formula (b-1) include anions represented by formulae (b1) to (b9) shown below.

In the formulae, q1 and q2 each independently represents an integer of 1 to 5; q3 represents an integer of 1 to 12; t3 represents an integer of 1 to 3; r1 and r2 each independently represents an integer of 0 to 3; g represents an integer of 1 to 20; R⁷ represents a substituent; n1 to n6 each independently represents 0 or 1; v0 to v6 each independently represents an integer of 0 to 3; w1 to w6 each independently represents an integer of 0 to 3; and Q″ is the same as defined above.

Examples of the substituent for R⁷ include the aforementioned substituents which may substitute part of the hydrogen atoms bonded to the carbon atoms constituting the ring structure of the aliphatic cyclic group explained above for R¹⁰¹, and the substituents which may substitute a hydrogen atom bonded to the aromatic ring contained in the aforementioned aromatic hydrocarbon group.

If there are two or more of the R⁷ group, as indicated by the values r1, r2, and w1 to w6, then the two or more of the R⁷ groups may be the same or different from each other.

{Cation Moiety}

M^(m+) represents an organic cation having a valency of m.

The organic cation for M^(m+) having a valency of m is not particularly limited, and an organic cation conventionally known as the cation moiety of an onium salt acid generator for a resist composition can be used.

The organic cation having a valency of m is preferably a sulfonium cation or a iodonium cation, and cations represented by general formulae (ca-1) to (ca-4) shown below are most preferable.

In the formulae, R²⁰¹ to R²⁰⁷ and R²¹⁰ to R²¹² independently represents an aryl group, an alkyl group or an alkenyl group, provided that two of R²⁰¹ to R²⁰³, R²⁰⁶ and R²⁰⁷, or R²¹¹ and R²¹² may be mutually bonded to form a ring with the sulfur atom; R²⁰⁸ and R²⁰⁹ each independently represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms; L²⁰¹ represents —C(═O)— or —C(═O)O—; each Y²⁰¹ independently represents an arylene group, an alkylene group or an alkenylene group; x represents 1 or 2; and W²⁰¹ represents a linking group having a valency of (x+1).

Examples of the aryl group for R²⁰¹ to R²⁰⁷ and R²¹⁰ to R²¹² include unsubstituted aryl groups of 6 to 20 carbon atoms, and a phenyl group or a naphthyl group is preferable.

The alkyl group for R²⁰¹ to R²⁰⁷ and R²¹⁰ to R²¹² is preferably a chain-like or cyclic alkyl group having 1 to 30 carbon atoms.

The alkenyl group for R²⁰¹ to R²⁰⁷ and R²¹⁰ to R²¹² preferably has 2 to 10 carbon atoms.

Examples of the substituent for R²⁰¹ to R²⁰⁷ and R²¹⁰ to R²¹² include an alkyl group, a halogen atom, a halogenated alkyl group, an oxo group (═O), a cyano group, an amino group, an aryl group and groups represented by general formulae (c1-r-1) to (ca-r-6) shown below.

In the formulae, each R′²⁰¹ independently represents a hydrogen atom or a hydrocarbon group of 1 to 30 carbon atoms.

The hydrocarbon group for R′²⁰¹ is the same as defined for the cyclic group which may have substituent, the chain-like alkyl group which may have substituent or the chain-like alkenyl group for R¹⁰¹.

When two of R²⁰¹ to R²⁰³, R²⁰⁶ and R²⁰⁷ or R²¹¹ and R²¹² are mutually bonded to form a ring with the sulfur atom, the groups may be bonded via a hetero atom such as a sulfur atom, an oxygen atom or a nitrogen atom or a functional group such as a carbonyl group, —SO—, —SO₂—, —SO₃—, —COO—, —CONH— or —N(R_(N))— (wherein R_(N) represents an alkyl group of 1 to 5 carbon atoms).

The ring containing the sulfur atom in the skeleton thereof is preferably a 3 to 10-membered ring, and most preferably a 5 to 7-membered ring.

Specific examples of the ring formed include a thiophene ring, a thiazole ring, a benzothiophene ring, a thianthrene ring, a benzothiophene ring, a dibenzothiophene ring, a 9H-thioxanthene ring, a thioxanthone ring, a phenoxathiin ring, a tetrahydrothiophenium ring, and a tetrahydrothiopyranium ring.

x represents 1 or 2.

W²⁰¹ represents a linking group having a valency of (x+1), i.e., a divalent or trivalent linking group.

The divalent linking group for W²⁰¹ is the same as defined for the divalent linking group for R²⁹, and may be linear, branched or cyclic, preferably cyclic. Among these, an arylene group having two carbonyl groups, each bonded to the terminal thereof is preferable.

Examples of the arylene group include a phenylene group and a naphthylene group, and a phenylene group is particularly desirable.

Examples of the trivalent linking group for W²⁰¹ include a group in which one hydrogen atom has been removed from a divalent linking group, and a group in which a divalent linking group is bonded to a divalent linking group. The divalent linking group is the same as defined for the divalent linking group for R²⁹. The trivalent linking group for W¹ is preferably a group in which 3 carbonyl groups are combined with an arylene group.

Specific examples of preferable cations represented by the formula (ca-1) include cations represented by formulae shown below.

In the formulae, g1, g2 and g3 represent recurring numbers, wherein g1 is an integer of 1 to 5, g2 is an integer of 0 to 20, and g3 is an integer of 0 to 20.

In the formula, Rd represents a hydrogen atom or a substituent, wherein the substituent is the same as defined for the substituent for R²⁰¹ to R²⁰⁷ and R²¹⁰ to R²¹².

As the organic cation for M^(m+), an organic cation represented by the aforementioned formula (c-1) or (c-3) is preferable.

Oxime sulfonate acid generators disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 9-208554 (Chemical Formulas 18 and 19 shown in paragraphs [0012] to [0014]) and oxime sulfonate acid generators disclosed in WO 2004/074242A2 (Examples 1 to 40 described at pages 65 to 86) may be preferably used.

Diazomethane acid generators disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-035551, Japanese Unexamined Patent Application, First Publication No. Hei 11-035552 and Japanese Unexamined Patent Application, First Publication No. Hei 11-035573 may be preferably used.

Furthermore, as examples of poly(bis-sulfonyl)diazomethanes, those disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-322707, including 1,3-bis(phenylsulfonyldiazomethylsulfonyl)propane, 1,4-bis(phenylsulfonyldiazomethylsulfonyl)butane, 1,6-bis(phenylsulfonyldiazomethylsulfonyl)hexane, 1,10-bis(phenylsulfonyldiazomethylsulfonyl)decane, 1,2-bis(cyclohexylsulfonyldiazomethylsulfonyl)ethane, 1,3-bis(cyclohexylsulfonyldiazomethylsulfonyl)propane, 1,6-bis(cyclohexylsulfonyldiazomethylsulfonyl)hexane, and 1,10-bis(cyclohexylsulfonyldiazomethylsulfonyl)decane, may be given.

As the component (B), one type of these acid generators may be used alone, or two or more types may be used in combination.

In the resist composition, the amount of the component (B), relative to 100 parts by weight of the component (A) is preferably from 0.5 to 60 parts by weight, more preferably from 1 to 50 parts by weight, and most preferably from 1 to 40 parts by weight. When the amount of the component (B) is within the above-mentioned range, formation of a resist pattern can be satisfactorily performed. Further, by virtue of the above-mentioned range, when each of the components are dissolved in an organic solvent, a uniform solution can be obtained and the storage stability becomes satisfactory.

<Optional Components>

[Component (D)]

The resist composition of the present invention may contain a basic-compound component (D) (hereafter referred to as the component (D)) as an optional component. In the present invention, the component (D) functions as an acid diffusion control agent, i.e., a quencher which traps the acid generated from the component (B) upon exposure. In the present invention, a “basic compound” refers to a compound which is basic relative to the component (B).

In the present invention, the component (D) may be a basic compound (D1) (hereafter, referred to as “component (D1)”) which has a cation moiety and an anion moiety, or a basic compound (D2) (hereafter, referred to as “component (D2)”) which does not fall under the definition of component (D1).

(Component (D1))

In the present invention, the component (D1) preferably contains at least one member selected from the group consisting of a compound (d1-1) represented by general formula (d1-1) shown below (hereafter, referred to as “component (d1-1)”), a compound (d1-2) represented by general formula (d1-2) shown below (hereafter, referred to as “component (d1-2)”) and a compound (d1-3) represented by general formula (d1-3) shown below (hereafter, referred to as “component (d1-3)”).

In the formulae, R⁵¹ represents a hydrocarbon group which may have a substituent; Z^(2c) represents a hydrocarbon group of 1 to 30 carbon atoms which may have a substituent (provided that the carbon adjacent to S has no fluorine atom as a substituent); R⁵² represents an organic group; Y⁵ represents a linear, branched or cyclic alkylene group or an arylene group; Rf represents a hydrocarbon group containing a fluorine atom; and each M⁺ independently represents an organic cation.

{Component (d1-1)}

Anion Moiety

In formula (d1-1), R⁵¹ represents a hydrocarbon group which may have a substituent.

The hydrocarbon group for R⁵¹ which may have a substituent may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and the same aliphatic hydrocarbon groups and aromatic hydrocarbon groups as those described above for the aforementioned R¹⁰¹ in the component (B) can be used.

Among these, as the hydrocarbon group for R⁵¹ which may have a substituent, an aromatic hydrocarbon group which may have a substituent or an aliphatic cyclic group which may have a substituent is preferable, and a phenyl group or a naphthyl group which may have a substituent, or a group in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane is more preferable.

As the hydrocarbon group for R⁵¹ which may have a substituent, a linear, branched or alicyclic alkyl group or a fluorinated alkyl group is also preferable.

The linear, branched or alicyclic alkyl group for R⁵¹ preferably has 1 to 10 carbon atoms, and specific examples thereof include a linear alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl or a decyl group, a branched alkyl group such as a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group or a 4-methylpentyl group, and an alicyclic alkyl group such as a norbornyl group or an adamantyl group.

The fluorinated alkyl group for R⁵¹ may be either chain-like or cyclic, but is preferably linear or branched.

The fluorinated alkyl group preferably has 1 to 11 carbon atoms, more preferably 1 to 8, and still more preferably 1 to 4. Specific examples include a group in which part or all of the hydrogen atoms constituting a linear alkyl group (such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group or a decyl group) have been substituted with fluorine atom(s), and a group in which part or all of the hydrogen atoms constituting a branched alkyl group (such as a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group or a 3-methylbutyl group) have been substituted with fluorine atom(s).

The fluorinated alkyl group for R⁵¹ may contain an atom other than fluorine. Examples of the atom other than fluorine include an oxygen atom, a carbon atom, a hydrogen atom, an oxygen atom, a sulfur atom and a nitrogen atom.

Among these, as the fluorinated alkyl group for R⁵¹, a group in which part or all of the hydrogen atoms constituting a linear alkyl group have been substituted with fluorine atom(s) is preferable, and a group in which all of the hydrogen atoms constituting a linear alkyl group have been substituted with fluorine atoms (i.e., a perfluoroalkyl group) is more preferable.

Specific examples of preferable anion moieties for the component (d1-1) are shown below.

Cation Moiety

In formula (d1-1), M⁺ represents an organic cation.

The organic cation for M⁺ is not particularly limited, and examples thereof include the same cation moieties as those of compounds represented by the aforementioned formula (b-1) or (b-2), and cation moieties represented by the aforementioned formulae (ca-1-1) to (ca-1-46) are preferable.

As the component (d1-1), one type of compound may be used, or two or more types of compounds may be used in combination.

{Component (d1-2)}

Anion Moiety

In formula (d1-2), Z^(2c) represents a hydrocarbon group of 1 to 30 carbon atoms which may have a substituent.

The hydrocarbon group of 1 to 30 carbon atoms for Z^(2c) which may have a substituent may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and the same aliphatic hydrocarbon groups and aromatic hydrocarbon groups as those described above for the aforementioned X³ in the component (B) can be used.

Among these, as the hydrocarbon group for Z^(2c) which may have a substituent, an aliphatic cyclic group which may have a substituent is preferable, and a group in which one or more hydrogen atoms have been removed from adamantane, norbornane, isobornane, tricyclodecane, tetracyclododecane or camphor (which may have a substituent) is more preferable.

The hydrocarbon group for Z^(2c) may have a substituent, and the same substituents as those described above for R¹⁰¹ in the aforementioned component (B) can be used. However, in Z^(2c), the carbon adjacent to the S atom within SO₃ ⁻ has no fluorine atom as a substituent. By virtue of SO₃ ⁻ having no fluorine atom adjacent thereto, the anion of the component (d1-2) becomes an appropriately weak acid anion, thereby improving the quenching ability of the component (D).

Specific examples of preferable anion moieties for the component (d1-2) are shown below.

Cation Moiety

In formula (d1-2), M⁺ is the same as defined for M⁺ in the aforementioned formula (d1-1).

As the component (d1-2), one type of compound may be used, or two or more types of compounds may be used in combination.

{Component (d1-3)}

Anion Moiety

In formula (d1-3), R⁵² represents an organic group. The organic group for R⁵² is not particularly limited, and examples thereof include an alkyl group, an alkoxy group, —O—C(═O)—C(R^(C2))═CH₂ (R^(C2) represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms) and —O—C(═O)—R^(C3) (R^(C3) represents a hydrocarbon group).

The alkyl group for R⁵² is preferably a linear or branched alkyl group of 1 to 5 carbon atoms, and specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group. Part of the hydrogen atoms within the alkyl group for R⁵² may be substituted with a hydroxy group, a cyano group or the like.

The alkoxy group for R⁵² is preferably an alkoxy group of 1 to 5 carbon atoms, and specific examples thereof include a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group and a tert-butoxy group. Among these, a methoxy group and an ethoxy group are particularly desirable.

When R⁵² is —O—C(═O)—C(R^(C2))═CH₂, R^(C2) represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms.

The alkyl group of 1 to 5 carbon atoms for R^(C2) is preferably a linear or branched alkyl group of 1 to 5 carbon atoms, and specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group and a neopentyl group.

The halogenated alkyl group for R^(C2) is a group in which part or all of the hydrogen atoms of the aforementioned alkyl group of 1 to 5 carbon atoms has been substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable.

As R^(C2), a hydrogen atom, an alkyl group of 1 to 3 carbon atoms or a fluorinated alkyl group of 1 to 3 carbon atoms is preferable, and a hydrogen atom or a methyl group is particularly desirable in terms of industrial availability.

When R⁵² is —O—C(═O)—R^(C3), R^(C3) represents a hydrocarbon group.

The hydrocarbon group for R^(C3) may be either an aromatic hydrocarbon group or an aliphatic hydrocarbon group. Specific examples of the hydrocarbon group for R^(C3) include the same hydrocarbon groups as those described for R¹⁰¹ in the component (B).

Among these, as the hydrocarbon group for R^(C3), an alicyclic group (e.g., a group in which one or more hydrogen atoms have been removed from a cycloalkane such as cyclopentane, cyclohexane, adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane) or an aromatic group (e.g., a phenyl group or a naphthyl group) is preferable. When R^(C3) is an alicyclic group, the resist composition can be satisfactorily dissolved in an organic solvent, thereby improving the lithography properties. Alternatively, when R^(C3) is an aromatic group, the resist composition exhibits an excellent photoabsorption efficiency in a lithography process using EUV or the like as the exposure source, thereby resulting in the improvement of the sensitivity and the lithography properties.

Among these, as R⁵², —O—C(═O)—C(R^(C2)′)═CH₂ (R^(C2)′ represents a hydrogen atom or a methyl group) or —O—C(═O)—R^(C3)′ (R^(C3)′ represents an aliphatic cyclic group) is preferable.

In formula (d1-3), Y⁵ represents a linear, branched or cyclic alkylene group or an arylene group.

Examples of the linear, branched or cyclic alkylene group or the arylene group for Y⁵ include the “linear or branched aliphatic hydrocarbon group”, “cyclic aliphatic hydrocarbon group” and “aromatic hydrocarbon group” described above as the divalent linking group for Y¹ or Y² in the aforementioned formula (a0-1).

Among these, as Y⁵, an alkylene group is preferable, a linear or branched alkylene group is more preferable, and a methylene group or an ethylene group is still more preferable.

In formula (d1-3), Rf represents a hydrocarbon group containing a fluorine atom.

The hydrocarbon group containing a fluorine atom for Rf is preferably a fluorinated alkyl group, and more preferably the same fluorinated alkyl groups as those described above for R⁵¹.

Specific examples of preferable anion moieties for the component (d1-3) are shown below.

Cation Moiety

In formula (d1-3), M⁺ is the same as defined for M⁺ in the aforementioned formula (d1-1).

As the component (d1-3), one type of compound may be used, or two or more types of compounds may be used in combination.

The component (D1) may contain one of the aforementioned components (d1-1) to (d1-3), or at least two of the aforementioned components (d1-1) to (d1-3).

The total amount of the components (d1-1) to (d1-3) relative to 100 parts by weight of the component (A) is preferably within a range from 0.5 to 10.0 parts by weight, more preferably from 0.5 to 8.0 parts by weight, and still more preferably from 1.0 to 5.0 parts by weight. When the amount of at least as large as the lower limit of the above-mentioned range, excellent lithography properties and excellent resist pattern shape can be obtained. On the other hand, when the amount of the component (D) is no more than the upper limit of the above-mentioned range, sensitivity can be maintained at a satisfactory level, and through-top becomes excellent.

{Production Method of Component (D1)}

In the present invention, the production methods of the components (d1-1) and (d1-2) are not particularly limited, and the components (d1-1) and (d1-2) can be produced by conventional methods.

Further, the production method of the component (d1-3) is not particularly limited. For example, in the case where R⁵² in formula (d1-3) is a group having an oxygen atom on the terminal thereof which is bonded to Y⁵, the compound (d1-3) represented by general formula (d1-3) can be produced by reacting a compound (i-1) represented by general formula (i-1) shown below with a compound (i-2) represented by general formula (i-2) shown below to obtain a compound (i-3) represented by general formula (i-3), and reacting the compound (i-3) with a compound Z⁻M⁺ having the desired cation M⁺, thereby obtaining the compound (d1-3).

In the formulae, R⁵², Y⁵, Rf and M⁺ are the same as defined for R⁵²Y⁵ Rf and M⁺ in the aforementioned general formula (d1-3), respectively; R^(52a) represents a group in which the terminal oxygen atom has been removed from R⁵²; and Z⁻ represents a counteranion.

Firstly, the compound (i-1) is reacted with the compound (i-2), to thereby obtain the compound (i-3).

In formula (i-1), R⁵² is the same as defined above, and R^(52a) represents a group in which the terminal oxygen atom has been removed from R⁵². In formula (i-2), Y⁵ and Rf are the same as defined above.

As the compound (i-1) and the compound (i-2), commercially available compounds may be used, or the compounds may be synthesized.

The method for reacting the compound (i-1) with the compound (i-2) to obtain the compound (i-3) is not particularly limited, but can be performed, for example, by reacting the compound (i-1) with the compound (i-2) in an organic solvent in the presence of an appropriate acidic catalyst, followed by washing and recovering the reaction mixture.

The acidic catalyst used in the above reaction is not particularly limited, and examples thereof include toluenesulfonic acid and the like. The amount of the acidic catalyst is preferably 0.05 to 5 moles, per 1 mole of the compound (i-2).

As the organic solvent used in the above reaction, any organic solvent which is capable of dissolving the raw materials, i.e., the compound (i-1) and the compound (i-2) can be used, and specific examples thereof include toluene and the like. The amount of the organic solvent is preferably 0.5 to 100 parts by weight, more preferably 0.5 to 20 parts by weight, relative to the amount of the compound (i-1). As the solvent, one type may be used alone, or two or more types may be used in combination.

In general, the amount of the compound (i-2) used in the above reaction is preferably 0.5 to 5 moles per 1 mole of the compound (i-1), and more preferably 0.8 to 4 moles per 1 mole of the compound (i-1).

The reaction time depends on the reactivity of the compounds (i-1) and (i-2), the reaction temperature or the like. However, in general, the reaction time is preferably 1 to 80 hours, and more preferably 3 to 60 hours.

The reaction temperature in the above reaction is preferably 20 to 200° C., and more preferably 20 to 150° C.

Next, the obtained compound (i-3) is reacted with the compound (i-4), thereby obtaining the compound (d1-3).

In formula (i-4), M⁺ is the same as defined above, and Z⁻ represents a counteranion.

The method for reacting the compound (i-3) with the compound (i-4) to obtain the compound (d1-3) is not particularly limited, but can be performed, for example, by dissolving the compound (i-3) in an organic solvent and water in the presence of an appropriate alkali metal hydroxide, followed by addition of the compound (i-4) and stirring.

The alkali metal hydroxide used in the above reaction is not particularly limited, and examples thereof include sodium hydroxide, potassium hydroxide and the like. The amount of the alkali metal hydroxide is preferably 0.3 to 3 moles, per 1 mole of the compound (i-3).

Examples of the organic solvent used in the above reaction include dichloromethane, chloroform, ethyl acetate and the like. The amount of the organic solvent is preferably 0.5 to 100 parts by weight, and more preferably 0.5 to 20 parts by weight, relative to the weight of the compound (i-3). As the solvent, one type may be used alone, or two or more types may be used in combination.

In general, the amount of the compound (i-4) used in the above reaction is preferably 0.5 to 5 moles per 1 mole of the compound (i-3), and more preferably 0.8 to 4 moles per 1 mole of the compound (i-3).

The reaction time depends on the reactivity of the compounds (i-3) and (i-4), the reaction temperature or the like. However, in general, the reaction time is preferably 1 to 80 hours, and more preferably 3 to 60 hours.

The reaction temperature in the above reaction is preferably 20 to 200° C., and more preferably 20 to 150° C.

After the reaction, the compound (d1-3) contained in the reaction mixture may be separated and purified. The separation and purification can be conducted by a conventional method. For example, any one of concentration, solvent extraction, distillation, crystallization, recrystallization and chromatography can be used alone, or two or more of these methods may be used in combination.

The structure of the compound (d1-3) obtained in the manner described above can be confirmed by a general organic analysis method such as ¹H-nuclear magnetic resonance (NMR) spectrometry, ¹³C-NMR spectrometry, ¹⁹F-NMR spectrometry, infrared absorption (IR) spectrometry, mass spectrometry (MS), elementary analysis and X-ray diffraction analysis.

(Component (D2))

The component (D2) is not particularly limited, as long as it is a compound which is basic relative to the component (B), so as to functions as an acid diffusion inhibitor, and does not fall under the definition of the component (D1). As the component (D2), any of the conventionally known compounds may be selected for use. Examples thereof include an aliphatic amine and an aromatic amine. Among these, an aliphatic amine is preferable, and a secondary aliphatic amine or tertiary aliphatic amine is particularly desirable.

An aliphatic amine is an amine having one or more aliphatic groups, and the aliphatic groups preferably have 1 to 12 carbon atoms.

Examples of these aliphatic amines include amines in which at least one hydrogen atom of ammonia (NH₃) has been substituted with an alkyl group or hydroxyalkyl group of no more than 12 carbon atoms (i.e., alkylamines or alkylalcoholamines), and cyclic amines.

Specific examples of alkylamines and alkylalcoholamines include monoalkylamines such as n-hexylamine, n-heptylamine, n-octylamine, n-nonylamine, and n-decylamine; dialkylamines such as diethylamine, di-n-propylamine, di-n-heptylamine, di-n-octylamine, and dicyclohexylamine; trialkylamines such as trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, tri-n-hexylamine, tri-n-pentylamine, tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamine, tri-n-decylamine, and tri-n-dodecylamine; and alkyl alcohol amines such as diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine, di-n-octanolamine, and tri-n-octanolamine. Among these, trialkylamines of 5 to 10 carbon atoms are preferable, and tri-n-pentylamine and tri-n-octylamine are particularly desirable.

Examples of the cyclic amine include heterocyclic compounds containing a nitrogen atom as a hetero atom. The heterocyclic compound may be a monocyclic compound (aliphatic monocyclic amine), or a polycyclic compound (aliphatic polycyclic amine).

Specific examples of the aliphatic monocyclic amine include piperidine, and piperazine.

The aliphatic polycyclic amine preferably has 6 to 10 carbon atoms, and specific examples thereof include 1,5-diazabicyclo[4.3.0]-5-nonene, 1,8-diazabicyclo[5.4.0]-7-undecene, hexamethylenetetramine, and 1,4-diazabicyclo[2.2.2]octane.

Examples of other aliphatic amines include tris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxyethoxy)ethyl}amine, tris{2-(2-methoxyethoxymethoxy)ethyl}amine, tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine, tris{2-(1-ethoxypropoxy)ethyl}amine, tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine and triethanolamine triacetate, and triethanolamine triacetate is preferable.

Examples of aromatic amines include aniline, pyridine, 4-dimethylaminopyridine, pyrrole, indole, pyrazole, imidazole and derivatives thereof, as well as diphenylamine, triphenylamine, tribenzylamine, 2,6-diisopropylaniline and N-tert-butoxycarbonylpyrrolidine.

As the component (D2), one type of compound may be used alone, or two or more types may be used in combination.

The component (D2) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A). When the amount of the component (D) is within the above-mentioned range, the shape of the resist pattern and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer are improved.

As the component (D), one type of compound may be used, or two or more types of compounds may be used in combination.

When the resist composition of the present invention contains the component (D), the amount of the component (D) relative to 100 parts by weight of the component (A) is preferably within a range from 0.1 to 15 parts by weight, more preferably from 0.3 to 12 parts by weight, and still more preferably from 0.5 to 10 parts by weight. When the amount of the component (C1) is at least as large as the lower limit of the above-mentioned range, various lithography properties (such as roughness) of the positive resist composition are improved. Further, a resist pattern having an excellent shape can be obtained. On the other hand, when the amount of the component (D) is no more than the upper limit of the above-mentioned range, sensitivity can be maintained at a satisfactory level, and through-top becomes excellent.

[Component (E)]

Furthermore, in the resist composition of the present invention, for preventing any deterioration in sensitivity, and improving the resist pattern shape and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer, at least one compound (E) (hereafter referred to as the component (E)) selected from the group consisting of an organic carboxylic acid, or a phosphorus oxo acid or derivative thereof can be added.

Examples of suitable organic carboxylic acids include acetic acid, malonic acid, citric acid, malic acid, succinic acid, benzoic acid, and salicylic acid.

Examples of phosphorus oxo acids include phosphoric acid, phosphonic acid and phosphinic acid. Among these, phosphonic acid is particularly desirable.

Examples of oxo acid derivatives include esters in which a hydrogen atom within the above-mentioned oxo acids is substituted with a hydrocarbon group. Examples of the hydrocarbon group include an alkyl group of 1 to 5 carbon atoms and an aryl group of 6 to 15 carbon atoms.

Examples of phosphoric acid derivatives include phosphoric acid esters such as di-n-butyl phosphate and diphenyl phosphate.

Examples of phosphonic acid derivatives include phosphonic acid esters such as dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonic acid, diphenyl phosphonate and dibenzyl phosphonate.

Examples of phosphinic acid derivatives include phosphinic acid esters and phenylphosphinic acid.

As the component (E), one type may be used alone, or two or more types may be used in combination.

The component (E) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A).

<Component (F)>

The resist composition of the present invention may contain a fluorine additive (hereafter, referred to as “component (F)”) for imparting water repellency to the resist film. As the component (F), for example, a fluorine-containing polymeric compound described in Japanese Unexamined Patent Application, First Publication No. 2010-002870.

Specific examples of the component (F) include polymers having a structural unit (f1) represented by general formula (f1-1) shown below. As such polymer, a polymer (homopolymer) consisting of a structural unit (f1); a copolymer of a structural unit (f1) and the aforementioned structural unit (a1); and a copolymer of a structural unit (f1), a structural unit derived from acrylic acid or methacrylic acid and the aforementioned structural unit (a1) are preferable. As the structural unit (a1) to be copolymerized with a structural unit (f1), a structural unit represented by the aforementioned formula (a1-0-1) is preferable, and a structural unit represented by the aforementioned formula (a1-1-32) is particularly desirable.

In the formula, R is the same as defined above; R⁴⁵ and R⁴⁶ each independently represents a hydrogen atom, a halogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms, provided that the plurality of R⁴⁵ and R⁴⁶ may be the same or different; a1 represents an integer of 1 to 5; and R⁷″ represents an organic group containing a fluorine atom.

In formula (f1-1), R is the same as defined above. As R, a hydrogen atom or a methyl group is preferable.

In formula (f1-1), examples of the halogen atom for R⁴⁵ and R⁴⁶ include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable. Examples of the alkyl group of 1 to 5 carbon atoms for R⁴⁵ and R⁴⁶ include the same alkyl group of 1 to 5 carbon atoms for R defined above, and a methyl group or an ethyl group is preferable. Specific examples of the halogenated alkyl group of 1 to 5 carbon atoms represented by R⁴⁵ or R⁴⁶ include groups in which part or all of the hydrogen atoms of the aforementioned alkyl groups of 1 to 5 carbon atoms have been substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable. Among these, as R⁴⁵ and R⁴⁶, a hydrogen atom, a fluorine atom or an alkyl group of 1 to 5 carbon atoms is preferable, and a hydrogen atom, a fluorine atom, a methyl group or an ethyl group is more preferable.

In formula (f1-1), a1 represents an integer of 1 to 5, preferably an integer of 1 to 3, and more preferably 1 or 2.

In formula (f1-1), R⁷″ represents an organic group containing a fluorine atom, and is preferably a hydrocarbon group containing a fluorine atom.

The hydrocarbon group containing a fluorine atom may be linear, branched or cyclic, and preferably has 1 to 20 carbon atoms, more preferably 1 to 15 carbon atoms, and most preferably 1 to 10 carbon atoms.

It is preferable that the hydrocarbon group having a fluorine atom has 25% or more of the hydrogen atoms within the hydrocarbon group fluorinated, more preferably 50% or more, and most preferably 60% or more, as the hydrophobicity of the resist film during immersion exposure is enhanced.

Among these, as R⁷″, a fluorinated hydrocarbon group of 1 to 5 carbon atoms is preferable, and a methyl group, —CH₂—CF₃, —CH₂—CF₂—CF₃, —CH(CF₃)₂, —CH₂—CH₂—CF₃, and —CH₂—CH₂—CF₂—CF₂—CF₂—CF₃ are most preferable.

The weight average molecular weight (Mw) (the polystyrene equivalent value determined by gel permeation chromatography) of the component (F) is preferably 1,000 to 50,000, more preferably 5,000 to 40,000, and most preferably 10,000 to 30,000. When the weight average molecular weight is no more than the upper limit of the above-mentioned range, the resist composition exhibits a satisfactory solubility in a resist solvent. On the other hand, when the weight average molecular weight is at least as large as the lower limit of the above-mentioned range, dry etching resistance and the cross-sectional shape of the resist pattern becomes satisfactory.

Further, the dispersity (Mw/Mn) of the component (F) is preferably 1.0 to 5.0, more preferably 1.0 to 3.0, and most preferably 1.2 to 2.5.

As the component (F), one type may be used alone, or two or more types may be used in combination.

The component (F) is typically used in an amount within a range from 0.5 to 10 parts by weight, relative to 100 parts by weight of the component (A).

[Component (S)]

The resist composition according to the present invention can be prepared by dissolving the materials for the resist composition in an organic solvent (hereafter, sometimes referred to as “component (S)”).

The component (S) may be any organic solvent which can dissolve the respective components to give a uniform solution, and one or more kinds of any organic solvent can be appropriately selected from those which have been conventionally known as solvents for a chemically amplified resist.

Examples thereof include lactones such as γ-butyrolactone; ketones such as acetone, methyl ethyl ketone (MEK), cyclohexanone, methyl-n-pentyl ketone, methyl isopentyl ketone, and 2-heptanone; polyhydric alcohols, such as ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol; compounds having an ester bond, such as ethylene glycol monoacetate, diethylene glycol monoacetate, propylene glycol monoacetate, and dipropylene glycol monoacetate; polyhydric alcohol derivatives including compounds having an ether bond, such as a monoalkylether (e.g., monomethylether, monoethylether, monopropylether or monobutylether) or monophenylether of any of these polyhydric alcohols or compounds having an ester bond (among these, propylene glycol monomethyl ether acetate (PGMEA) and propylene glycol monomethyl ether (PGME) are preferable); cyclic ethers such as dioxane; esters such as methyl lactate, ethyl lactate (EL), methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, and ethyl ethoxypropionate; aromatic organic solvents such as anisole, ethylbenzylether, cresylmethylether, diphenylether, dibenzylether, phenetole, butylphenylether, ethylbenzene, diethylbenzene, pentylbenzene, isopropylbenzene, toluene, xylene, cymene and mesitylene; and dimethylsulfoxide (DMSO).

These solvents can be used individually, or in combination as a mixed solvent.

Among these, PGMEA, PGME, γ-butyrolactone and EL are preferable.

Further, among the mixed solvents, a mixed solvent obtained by mixing PGMEA with a polar solvent is preferable. The mixing ratio (weight ratio) of the mixed solvent can be appropriately determined, taking into consideration the compatibility of the PGMEA with the polar solvent, but is preferably in the range of 1:9 to 9:1, more preferably from 2:8 to 8:2.

Specifically, when EL or cyclohexanone is mixed as the polar solvent, the PGMEA:EL or cyclohexanone weight ratio is preferably from 1:9 to 9:1, and more preferably from 2:8 to 8:2. Alternatively, when PGME is mixed as the polar solvent, the PGMEA:PGME weight ratio is preferably from 1:9 to 9:1, more preferably from 2:8 to 8:2, and still more preferably 3:7 to 7:3.

Further, as the component (5), a mixed solvent of at least one of PGMEA and EL with γ-butyrolactone is also preferable. The mixing ratio (former:latter) of such a mixed solvent is preferably from 70:30 to 95:5.

The amount of the component (S) is not particularly limited, and is appropriately adjusted to a concentration which enables coating of a coating solution to a substrate In general, the organic solvent is used in an amount such that the solid content of the resist composition becomes within the range from 1 to 20% by weight, and preferably from 2 to 15% by weight.

According to the resist composition of the present invention, a resist pattern exhibiting an excellent lithography properties can be formed by an alkali developing process and a solvent developing, negative-tone process using an organic developing solution. In particular, in the solvent developing, negative-tone process, line collapse (which becomes a problem) can be reduced, and miniaturization of resist patterns can be realized.

The reason why the above effects can be achieved is presumed that, by virtue of the component (A1) including a structural unit (a0) having a branched chain, the Tg of the entire resin is increased, thereby enabling to shorten the diffusion length of acid, and the solubility in a solvent is improved, thereby improving the rectangularity.

<<Method of Forming a Resist Pattern>>

More specifically, the method for forming a resist pattern according to a second aspect of the present invention can be performed, for example, as follows.

Firstly, the aforementioned resist composition is applied to a substrate using a spinner or the like, and a bake treatment (post applied bake (PAB)) is conducted at a temperature of 80 to 150° C. for 40 to 120 seconds, preferably 60 to 90 seconds, to form a resist film. Following selective exposure of the thus formed resist film, either by exposure through a mask having a predetermined pattern formed thereon (mask pattern) using an exposure apparatus such as an ArF exposure apparatus, an electron beam lithography apparatus or an EUV exposure apparatus, or by patterning via direct irradiation with an electron beam without using a mask pattern, baking treatment (post exposure baking (PEB)) is conducted under temperature conditions of 80 to 150° C. for 40 to 120 seconds, and preferably 60 to 90 seconds. The resulting resist film is subjected to developing treatment using an organic developing solution, preferably followed by rinsing with a rinse liquid containing an organic solvent, and then drying is conducted.

After the developing treatment or the rinsing, the developing solution or the rinse liquid remaining on the pattern can be removed by a treatment using a supercritical fluid.

If necessary, after the developing treatment, the rinsing or the treatment with a supercritical fluid, a bake treatment (post bake) may be conducted to remove any remaining organic solvent.

The substrate is not specifically limited and a conventionally known substrate can be used. For example, substrates for electronic components, and such substrates having wiring patterns formed thereon can be used. Specific examples of the material of the substrate include metals such as silicon wafer, copper, chromium, iron and aluminum; and glass. Suitable materials for the wiring pattern include copper, aluminum, nickel, and gold.

Further, as the substrate, any one of the above-mentioned substrates provided with an inorganic and/or organic film on the surface thereof may be used. As the inorganic film, an inorganic antireflection film (inorganic BARC) can be used. As the organic film, an organic antireflection film (organic BARC) and an organic film such as a lower-layer organic film used in a multilayer resist method can be used.

Here, a “multilayer resist method” is method in which at least one layer of an organic film (lower-layer organic film) and at least one layer of a resist film (upper resist film) are provided on a substrate, and a resist pattern formed on the upper resist film is used as a mask to conduct patterning of the lower-layer organic film. This method is considered as being capable of forming a pattern with a high aspect ratio. More specifically, in the multilayer resist method, a desired thickness can be ensured by the lower-layer organic film, and as a result, the thickness of the resist film can be reduced, and an extremely fine pattern with a high aspect ratio can be formed.

The multilayer resist method is broadly classified into a method in which a double-layer structure consisting of an upper-layer resist film and a lower-layer organic film is formed (double-layer resist method), and a method in which a multilayer structure having at least three layers consisting of an upper-layer resist film, a lower-layer organic film and at least one intermediate layer (thin metal film or the like) provided between the upper-layer resist film and the lower-layer organic film (triple-layer resist method).

The wavelength to be used for exposure is not particularly limited and the exposure can be conducted using radiation such as ArF excimer laser, KrF excimer laser, F₂ excimer laser, extreme ultraviolet rays (EUV), vacuum ultraviolet rays (VUV), electron beam (EB), X-rays, and soft X-rays. The resist composition of the present invention is effective to KrF excimer laser, ArF excimer laser, EB and EUV, and particularly effective to ArF excimer laser, EB and EUV.

The exposure of the resist film can be either a general exposure (dry exposure) conducted in air or an inert gas such as nitrogen, or immersion exposure (immersion lithography).

In immersion lithography, the region between the resist film and the lens at the lowermost point of the exposure apparatus is pre-filled with a solvent (immersion medium) that has a larger refractive index than the refractive index of air, and the exposure (immersion exposure) is conducted in this state.

The immersion medium preferably exhibits a refractive index larger than the refractive index of air but smaller than the refractive index of the resist film to be exposed. The refractive index of the immersion medium is not particularly limited as long at it satisfies the above-mentioned requirements.

Examples of this immersion medium which exhibits a refractive index that is larger than the refractive index of air but smaller than the refractive index of the resist film include water, fluorine-based inert liquids, silicon-based solvents and hydrocarbon-based solvents.

Specific examples of the fluorine-based inert liquids include liquids containing a fluorine-based compound such as C₃HCl₂F₅, C₄F₉OCH₃, C₄F₉OC₂H₅ or C₅H₃F₇ as the main component, which have a boiling point within a range from 70 to 180° C. and preferably from 80 to 160° C. A fluorine-based inert liquid having a boiling point within the above-mentioned range is advantageous in that the removal of the immersion medium after the exposure can be conducted by a simple method.

As a fluorine-based inert liquid, a perfluoroalkyl compound in which all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is particularly desirable. Examples of these perfluoroalkyl compounds include perfluoroalkylether compounds and perfluoroalkylamine compounds.

Specifically, one example of a suitable perfluoroalkylether compound is perfluoro(2-butyl-tetrahydrofuran) (boiling point 102° C.), and an example of a suitable perfluoroalkylamine compound is perfluorotributylamine (boiling point 174° C.).

As the immersion medium, water is preferable in terms of cost, safety, environment and versatility.

As an example of the alkali developing solution used in an alkali developing process, a 0.1 to 10% by weight aqueous solution of tetramethylammonium hydroxide (TMAH) can be given.

As the organic solvent contained in the organic developing solution used in a solvent developing process, any of the conventional organic solvents can be used which are capable of dissolving the component (A) (prior to exposure). Specific examples of the organic solvent include polar solvents such as ketone solvents, ester solvents, alcohol solvents, amide solvents and ether solvents, and hydrocarbon solvents.

If desired, the organic developing solution may have a conventional additive blended. Examples of the additive include surfactants. The surfactant is not particularly limited, and for example, an ionic or non-ionic fluorine and/or silicon surfactant can be used.

When a surfactant is added, the amount thereof based on the total amount of the organic developing solution is generally 0.001 to 5% by weight, preferably 0.005 to 2% by weight, and more preferably 0.01 to 0.5% by weight.

The developing treatment can be performed by a conventional developing method. Examples thereof include a method in which the substrate is immersed in the developing solution for a predetermined time (a dip method), a method in which the developing solution is cast up on the surface of the substrate by surface tension and maintained for a predetermined period (a puddle method), a method in which the developing solution is sprayed onto the surface of the substrate (spray method), and a method in which the developing solution is continuously ejected from a developing solution ejecting nozzle while scanning at a constant rate to apply the developing solution to the substrate while rotating the substrate at a constant rate (dynamic dispense method).

As the organic solvent to be used as the developing solution in the solvent developing process, any of the conventional organic solvents can be appropriately selected for use which are capable of dissolving the base component (A) (prior to exposure of the base component (A)). Specific examples of the organic solvent include polar solvents such as ketone solvents, ester solvents, alcohol solvents, amide solvents, ether solvents and nitrile solvents, and hydrocarbon solvents. Among these, ester solvents, ketone solvents and nitrile solvents are preferable.

A ketone solvent is an organic solvent containing C—C(═O)—C within the structure thereof. An ester solvent is an organic solvent containing C—C(═O)—O—C within the structure thereof. An alcohol solvent is an organic solvent containing an alcoholic hydroxy group within the structure thereof, and an “alcoholic hydroxy group” refers to a hydroxy group bonded to a carbon atom of an aliphatic hydrocarbon group. An amide solvent is an organic solvent containing an amide group within the structure thereof. An ether solvent is an organic solvent containing C—O—C within the structure thereof. Some organic solvents have a plurality of the functional groups which characterizes the aforementioned solvents within the structure thereof. In such a case, the organic solvent can be classified as any type of the solvent having the characteristic functional group. For example, diethyleneglycol monomethylether can be classified as either an alcohol solvent or an ether solvent. A hydrocarbon solvent consists of a hydrocarbon, and does not have any substituent (atom or group other than hydrogen and carbon).

Specific examples of ketone solvents include 1-octanone, 2-octanone, 1-nonanone, 2-nonanone, acetone, 4-heptanone, 1-hexanone, 2-hexanone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, phenylacetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, acetonylacetone, ionone, diacetonylalcohol, acetylcarbinol, acetophenone, methyl naphthyl ketone, isophorone, propylenecarbonate, γ-butyrolactone and methyl amyl ketone (2-heptanone).

Examples of ester solvents include methyl acetate, butyl acetate, ethyl acetate, isopropyl acetate, amyl acetate, isoamyl acetate, ethyl methoxyacetate, ethyl ethoxyacetate, propylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monophenyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monopropyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monophenyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, 2-methoxybutyl acetate, 3-methoxybutyl acetate, 4-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, 3-ethyl-3-methoxybutyl acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, 2-ethoxybutyl acetate, 4-ethoxybutyl acetate, 4-propoxybutyl acetate, 2-methoxypentyl acetate, 3-methoxypentyl acetate, 4-methoxypentyl acetate, 2-methyl-3-methoxypentyl acetate, 3-methyl-3-methoxypentyl acetate, 3-methyl-4-methoxypentyl acetate, 4-methyl-4-methoxypentyl acetate, propylene glycol diacetate, methyl formate, ethyl formate, butyl formate, propyl formate, ethyl lactate, butyl lactate, propyl lactate, ethyl carbonate, propyl carbonate, butyl carbonate, methyl pyruvate, ethyl pyruvate, propyl pyruvate, butyl pyruvate, methyl acetoacetate, ethyl acetoacetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl 2-hydroxypropionate, ethyl 2-hydroxypropionate, methyl-3-methoxypropionate, ethyl-3-methoxypropionate, ethyl-3-ethoxypropionate and propyl-3-methoxypropionate.

As the ester solvent, a solvent represented by general formula (1) described later or a solvent represented by general formula (2) described later is preferable, a solvent represented by general formula (1) is more preferable, an alkyl acetate is still more preferable, and butyl acetate is particularly desirable.

Examples of nitrile solvents include acetonitrile, propionitrile, valeronitrile and butyronitrile.

If desired, the organic developing solution may have a conventional additive blended. Examples of the additive include surfactants. The surfactant is not particularly limited, and for example, an ionic or non-ionic fluorine and/or silicon surfactant can be used.

The development treatment using the organic developing solution can be performed by a conventional developing method. Examples thereof include a method in which the substrate is immersed in the developing solution for a predetermined time (a dip method), a method in which the developing solution is cast up on the surface of the substrate by surface tension and maintained for a predetermined period (a puddle method), a method in which the developing solution is sprayed onto the surface of the substrate (spray method), and a method in which the developing solution is continuously ejected from a developing solution ejecting nozzle while scanning at a constant rate to apply the developing solution to the substrate while rotating the substrate at a constant rate (dynamic dispense method).

After the developing treatment and before drying, a rinse treatment may be performed using a rinse liquid containing an organic solvent. By performing a rinse treatment, an excellent pattern can be formed.

As the organic solvent used for the rinse liquid, any of the aforementioned organic solvents for the organic developing solution can be used which hardly dissolve the pattern. In general, at least one solvent selected from the group consisting of hydrocarbon solvents, ketone solvents, ester solvents, alcohol solvents, amide solvents and ether solvents is used. Among these, at least one solvent selected from the group consisting of hydrocarbon solvents, ketone solvents, ester solvents, alcohol solvents and amide solvents is preferable, more preferably at least one solvent selected from the group consisting of alcohol solvents and ester solvents, and an alcohol solvent is particularly desirable.

The alcohol solvent used for the rinse liquid is preferably a monohydric alcohol of 6 to 8 carbon atoms, and the monohydric alcohol may be linear, branched or cyclic. Specific examples thereof include 1-hexanol, 1-heptanol, 1-octanol, 2-hexanol, 2-heptanol, 2-octanol, 3-hexanol, 3-heptanol, 3-octanol, 4-octanol and benzyl alcohol. Among these, 1-hexanol, 2-heptanol and 2-hexanol are preferable, and 1 hexanol and 2-hexanol are more preferable.

These organic solvents can be used individually, or at least 2 solvents may be mixed together. Further, an organic solvent other than the aforementioned examples or water may be mixed together. However, in consideration of the development characteristics, the amount of water within the rinse liquid, based on the total amount of the rinse liquid is preferably 30% by weight or less, more preferably 10% by weight or less, still more preferably 5% by weight or less, and most preferably 3% by weight or less.

If desired, the organic developing solution may have a conventional additive blended. Examples of the additive include surfactants. As the surfactant, the same surfactants as those described above can be mentioned, and a non-ionic surfactant is preferable, and a fluorine surfactant or a silicon surfactant is more preferable.

When a surfactant is added, the amount thereof based on the total amount of the rinse liquid is generally 0.001 to 5% by weight, preferably 0.005 to 2% by weight, and more preferably 0.01 to 0.5% by weight.

The rinse treatment (washing treatment) using the rinse liquid can be performed by a conventional rinse method. Examples thereof include a method in which the rinse liquid is continuously applied to the substrate while rotating it at a constant rate (rotational coating method), a method in which the substrate is immersed in the rinse liquid for a predetermined time (dip method), and a method in which the rinse liquid is sprayed onto the surface of the substrate (spray method).

EXAMPLES

The present invention will be described more specifically with reference to the following examples, although the scope of the present invention is by no way limited by these examples.

Polymer Synthesis Example

Polymeric compounds 1 to 20 were produced using the following monomers (1) to (13) which derived the structural units constituting each polymeric compound. The polymeric compound 1 was synthesized as follows, and the other polymeric compounds were synthesized by a conventional method. With respect to the obtained compounds, the compositional ratio (the molar ratio of the respective structural units indicated in the structural formula shown below) as determined by carbon 13 nuclear magnetic resonance spectroscopy (600 MHz ¹³C-NMR; internal standard: tetramethylsilane), and the weight average molecular weight (Mw) and the molecular weight dispersity (Mw/Mn) determined by the polystyrene equivalent value as measured by GPC are shown in Tables 1 and 2.

Polymer Synthesis Example 1 Synthesis of Polymeric Compound 1

In a separable flask equipped with a thermometer, a reflux tube and a nitrogen feeding pipe, 22.00 g (66.20 mmol) of the compound (1), 3.84 g (15.46 mmol) of a compound (3) and 3.76 g (15.90 mmol) of a compound (4) were dissolved in 76.81 g of methyl ethyl ketone to obtain a solution.

Then, 15.24 mmol of dimethyl 2,2′-azobis(isobutyrate) (V-601) as a polymerization initiator was added and dissolved in the resulting solution to obtain a dipping solution. Then, a solution obtained by dissolving 31.54 g (120.20 mmol) of a compound (2) in 42.61 g of methyl ethyl ketone was heated to 80° C., and the dipping solution was dropwise added thereto over 4 hours in a nitrogen atmosphere. Thereafter, the reaction solution was heated for 1 hour while stirring, and then cooled to room temperature. The obtained reaction polymer solution was dropwise added to an excess amount of methanol to deposit a polymer. Thereafter, the precipitated white powder was separated by filtration, followed by washing with methanol and drying, thereby obtaining 25.20 g of a polymeric compound 1 as an objective compound. With respect to the obtained polymeric compound, the weight average molecular weight (Mw) and the dispersity (Mw/Mn) were determined by the polystyrene equivalent value as measured by gel permeation chromatography (GPC). As a result, it was found that the weight average molecular weight was 4,300, and the dispersity was 1.39. Further, analysis was conducted by carbon 13 nuclear magnetic resonance spectroscopy (600 MHz, ¹³C-NMR) to determine the composition of the copolymer (ratio (molar ratio) of the respective structural units within the structural formula).

TABLE 1 Polymeric compound 1 2 3 4 5 6 7 8 9 10 Monomer (1) 47.1 35.5 25.2 40.2 (2) 37.7 36.6 10.1 19.5 37.5 10.3 18.8 (3) 4.9 4.8 5.3 (4) 10.3 8.9 9.2 11.3 21.3 8.6 10.7 9.3 12.7 21.1 (5) 49.7 42.8 (6) 45.2 45.4 (7) 31.5 31.1 (8) 12.5 12.6 (9) 38.5 39.5 (10) 41.1 (11) 7.5 (12) 100 46.5 35 24.8 39.4 (13) Mw 4300 5100 6900 7800 8000 6500 4800 7100 6800 7900 Mw/Mn 1.39 1.36 1.57 1.61 1.7 1.64 1.35 1.63 1.59 1.68

TABLE 2 Polymeric compound 11 12 13 14 15 16 17 18 19 20 Monomer (1) 51.6 50.8 10.5 11.2 (2) 43.2 (3) 43.2 (4) 8.8 8.9 8.9 (5) 50.3 50.7 (6) 49.2 (7) 25.8 25.6 25.8 25.4 (8) 49.2 (9) 48.4 49.7 50.4 49.3 51.0 (10) 40.5 (11) 6.9 (12) 43.8 50.8 10.5 11.0 (13) 11.6 12.8 11.6 12.6 Mw 6200 6600 8200 7500 9100 9300 5500 7500 9100 9300 Mw/Mn 1.54 1.6 1.64 1.59 1.68 1.71 1.57 1.59 1.68 1.71

TABLE 3 Component Component Component Component Component (A) (B) (D) (F) Component (S) (E) Ex. 1 (A)-1 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2] Ex. 2 (A)-2 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2] Ex. 3 (A)-3 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2] Ex. 4 (A)-4 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2] Ex. 5 (A)-5 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2] Ex. 6 (A)-6 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2] Comp. Ex. 1 (A)-7 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2] Comp. Ex. 2 (A)-8 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2] Comp. Ex. 3 (A)-9 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2] Comp. Ex. 4 (A)-10 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2] Comp. Ex. 5 (A)-11 (B)-1 (D)-1 (F)-1 (S)-1 (S)-2 (E)-1 [100] [12] [3] [3] [10] [2860] [2]

TABLE 4 Component Component Component Component Component (A) (B) (D) (F) Component (S) (E) Ex. 7 (A)-12 (B)-2 (D)-2 (F)-2 (S)-1 (S)-2 (E)-1 [100] [7] [3.5] [3] [100] [2860] [1] Ex. 8 (A)-13 (B)-2 (D)-2 (F)-2 (S)-1 (S)-2 (E)-1 [100] [7] [3.5] [3] [100] [2860] [1] Ex. 9 (A)-14 (B)-2 (D)-2 (F)-2 (S)-1 (S)-2 (E)-1 [100] [7] [3.5] [3] [100] [2860] [1] Ex. 10 (A)-15 (B)-2 (D)-2 (F)-2 (S)-1 (S)-2 (E)-1 [100] [7] [3.5] [3] [100] [2860] [1] Ex. 11 (A)-16 (B)-2 (D)-2 (F)-2 (S)-1 (S)-2 (E)-1 [100] [7] [3.5] [3] [100] [2860] [1] Comp. Ex. 6 (A)-17 (B)-2 (D)-2 (F)-2 (S)-1 (S)-2 (E)-1 [100] [7] [3.5] [3] [100] [2860] [1] Comp. Ex. 7 (A)-18 (B)-2 (D)-2 (F)-2 (S)-1 (S)-2 (E)-1 [100] [7] [3.5] [3] [100] [2860] [1] Comp. Ex. 8 (A)-19 (B)-2 (D)-2 (F)-2 (S)-1 (S)-2 (E)-1 [100] [7] [3.5] [3] [100] [2860] [1] Comp. Ex. 9 (A)-20 (B)-2 (D)-2 (F)-2 (S)-1 (S)-2 (E)-1 [100] [7] [3.5] [3] [100] [2860] [1]

In Tables 3 and 4, the reference characters indicate the following. The values in brackets [ ] indicate the amount (in terms of parts by weight) of the component added.

(A)-1 to (A)-20: the aforementioned polymeric compounds 1 to 20

(B)-1: a compound represented by structural formula (B)-1 shown below

(B)-2: a compound represented by structural formula (B)-2 shown below

(D)-1: a compound represented by structural formula (D)-1 shown below

(D)-2: a compound represented by structural formula (D)-2 shown below

(F)-1: a compound represented by structural formula (F)-1 shown below. l/m=8/2 (molar ratio). Mw: 25,900, Mw/Mn: 1.50.

(F)-2: a compound represented by structural formula (F)-2 shown below. l/m/n=7/2/1 (molar ratio). Mw: 16,600, Mw/Mn: 1.37.

(S)-1: γ-butyrolactone

(S)-2: a mixed solvent of PGMEA/PGME/cyclohexanone=45/30/25

(E)-1: salicylic acid

<<Method of Forming a Resist Pattern>>

An organic anti-reflection film composition (product name: ARC29A, manufactured by Brewer Science Ltd.) was applied to an 12-inch silicon wafer using a spinner, and the composition was then baked at 80° C. for 60 seconds, thereby forming an organic anti-reflection film having a film thickness of 100 nm.

Then, each of the resist compositions of Examples 1 to 6 and Comparative Examples 1 to 5 was applied to the organic anti-reflection film using a spinner, and was then prebaked (PAB) on a hotplate at 80° C. for 60 seconds and dried, thereby forming a resist film having a film thickness of 100 nm.

Subsequently, the resist film was selectively irradiated with an ArF excimer laser (193 nm) through a mask, using an ArF immersion exposure apparatus NSR-S609B (manufactured by Nikon Corporation, NA (numerical aperture)=1.07, Crosspole (0.78-0.97) with POLANO).

Next, a PEB treatment was conducted at 80° C. for 60 seconds, followed by alkali development for 10 seconds at 23° C. in a 2.38% by weight aqueous tetramethylammonium hydroxide (TMAH) solution (product name: NMD-3; manufactured by Tokyo Ohka Kogyo Co., Ltd.). Then, the resist was washed for 20 seconds with pure water, followed by drying by shaking.

As a result, a space and line pattern (SL pattern) having a line width of 65 nm and a pitch of 113.75 nm (hereafter, referred to as “Target 1”) was formed. Further, a space and line pattern having a space width of 75 nm and a pitch of 160 nm (hereafter, referred to as “Target 2”) was formed in the same manner. The optimum exposure dose Eop (mJ/cm²; sensitivity) with which each SL pattern was formed, and the MEEF were determined. The results are shown in Table 5.

Further, an organic anti-reflection film composition (product name: ARC29A, manufactured by Brewer Science Ltd.) was applied to an 8-inch silicon wafer using a spinner, and the composition was then baked on a hot plate at 105° C. for 60 seconds, thereby forming an organic anti-reflection film having a film thickness of 100 nm.

Then, each of the resist compositions of Examples 7 to 11 and Comparative Examples 6 to 9 was applied to the organic anti-reflection film using a spinner, and was then prebaked (PAB) on a hotplate at 105° C. for 60 seconds and dried, thereby forming a resist film having a film thickness of 100 nm.

Subsequently, the resist film was selectively irradiated with an ArF excimer laser through a half-tone mask, using an ArF immersion exposure apparatus NSR-S609B (manufactured by Nikon Corporation, NA (numerical aperture)=1.07, X pole (in/out=0.97/0.78) with Y-Polarization)). Next, PEB was conducted at 95° C. for 60 seconds, and development treatment was performed at 23° C. for 12 seconds using methyl n-amyl ketone, followed by drying by shaking.

As a result, in each of the examples, a 1:1 space and line pattern (SL pattern) having a space width of 48 nm and a pitch of 96 nm was formed on the resist film.

The optimum exposure dose Eop (mJ/cm²; sensitivity) with which the SL pattern was formed, the LER and the Max space were determined. The results are shown in Table 6.

[Evaluation of Pattern Shape]

The shape of the 1:1 SL pattern obtained in the manner as described above was evaluated.

A: Not T-top shaped

B: T-top shaped

The results are shown in Table 6.

[Evaluation of MEEF]

With the above Eop and fixing the pitch (in this case, since the SL pattern size was 49 nm, the pitch was fixed at 98 nm), the target size of the line pattern was changed at intervals of 1 nm, and SL patterns were formed with respect to 11 points. The value of MEEF was determined as the gradient of a graph obtained by plotting the target size (nm) (in this case, from 43 to 53 nm) on the horizontal axis, and the actual pattern size (nm) of the patterns formed using the mask patterns on the vertical axis. A MEEF value (gradient of the plotted line) closer to 1 indicates that a resist pattern faithful to the mask pattern was formed. The results are shown in Table 5.

[Evaluation of Line Edge Roughness (LER)]

With respect to the SL pattern formed in the above <Formation of resist pattern> having a space width of 48 nm and a pitch of 96 nm, 3σ was determined as a yardstick for indicating LER.

“3σ” indicates a value of 3 times the standard deviation (σ) (i.e., 3(s)) (unit: nm) determined by measuring the line width at 400 points in the lengthwise direction of the line using a scanning electron microscope (product name: S-9380, manufactured by Hitachi High-Technologies Corporation; acceleration voltage: 800V). The smaller this value is, the lower the level of roughness of the line side walls, indicating that an SL pattern with a uniform width was obtained. The results are indicated under “LER (nm)” in Table 6.

[Evaluation of Max Space]

With respect to the formed SL pattern having a space width of 48 nm and a pitch of 96 nm, the maximum value of the space width was measured when the exposure dose was reduced. Larger Max space indicates that an extremely fine line was formed. The results are shown in Table 6.

TABLE 5 Target-1 Target-2 PAB/PEB Eop Eop (° C.) (mJ/cm²) MEEF (mJ/cm²) MEEF Ex. 1 80/80 27.7 2.89 27.2 2.54 Ex. 2 80/80 32.8 2.77 29.2 2.44 Ex. 3 80/80 26.5 2.89 26.2 2.55 Ex. 4 100/95  25.6 2.68 25 2.39 Ex. 5 100/90  24.8 2.78 24.3 2.48 Ex. 6 80/80 22.1 2.87 23 2.56 Comp. Ex. 1 80/80 24.8 2.98 25.2 2.61 Comp. Ex. 2 80/80 24 3.05 24.5 2.7 Comp. Ex. 3 100/95  23.6 2.9 23.8 2.61 Comp. Ex. 4 100/90  23 2.99 23.2 2.68 Comp. Ex. 5 80/80 21.1 3.02 21.5 2.72

TABLE 6 PAB/PEB Eop LER Max Space (° C.) (mJ/cm²) (nm) (nm) Shape Ex. 7 105/95 32.5 5.38 55.4 A Ex. 8 105/95 41.6 5.57 54.3 A Ex. 9  95/85 27 5.21 58.9 A Ex. 10  95/85 28.4 5.67 53.1 A Ex. 11 100/90 29.1 5.44 53.8 A Comp. Ex. 6 105/95 28.5 6.35 48.5 B Comp. Ex. 7  95/85 24.3 6.26 49.5 B Comp. Ex. 8  95/85 25.6 6.77 48.4 B Comp. Ex. 9 100/90 26 6.65 48.7 B

While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims. 

What is claimed is:
 1. A resist composition comprising a base component (A) which exhibits changed solubility in a developing solution under the action of acid and an acid-generator component (B) which generates acid upon exposure, the base component (A) comprising a polymeric compound (A1) comprising a structural unit (a0) represented by general formula (a0-1) shown below and a structural unit (a1) containing an acid decomposable group which exhibits increased polarity by the action of acid:

wherein R¹ represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; W represents —COO—, a —CONH— group or a divalent aromatic hydrocarbon group; Y¹ and Y² each independently represents a divalent linking group or a single bond; R′¹ represents a hydrogen atom; R′² represents a methyl group; and R² is a group represented by general formula (3-1) shown below:

wherein A′ represents an oxygen atom; a represents an integer of 0 to 2; and R⁸ represents an alkyl group, an alkoxy group, a halogenated alkyl group, a hydroxyl group, —COOR″, —OC(═O)R″, a hydroxyalkl group or a cyano group, wherein R″ represents a hydrogen atom or an alkyl group.
 2. A method of forming a resist pattern, comprising: using a resist composition of claim 1 to form a resist film on a substrate; conducting exposure of the resist film; and developing the resist film to form a resist pattern. 